R2: redesign session store with wire-format identity

Replace the single-session SessionManager seam with a directory-backed
catalog. session_manager.zig -> file_system_jsonl_store.zig; the old
machinery becomes internal SessionFile, and a new FileSystemJSONLStore
implements the redesigned SessionStore vtable (create/list/resolve/latest/
load/appendMessages) minting Session/SessionInfo handles.

Session logs now record wire-format provider identity
({api_style, base_url, model, reasoning}) instead of a single provider
string or CLI aliases; no api_key material is ever stored. Disk* content
types renamed Stored*; the rich audit-oriented write record is
PersistentMessage (in-memory Message + WireIdentity + provenance).

Agent.init now takes a Session; persist_provider/persist_model display
strings deleted (banner stays alias-based, resume picks default model).
Message.metadata round-trips. Dangling-prompt recovery dropped. CLI
migrated to the catalog store for run/resume/list. Clean break, no version
bump (old logs wiped).

1 files changed, 0 insertions, 1886 deletions

diff --git a/libpanto/src/session_manager.zig b/libpanto/src/session_manager.zig
deleted file mode 100644
index b659506..0000000
--- a/libpanto/src/session_manager.zig
+++ /dev/null
@@ -1,1886 +0,0 @@
-//! Session lifecycle: create, open, replay, append.
-//!
-//! Backed by an append-only JSONL file on disk. The on-disk types live in
-//! `session.zig`. This module owns:
-//!
-//!   - Path resolution (sessions dir is supplied by the caller; we own the
-//!     filename and writes within it).
-//!   - The in-memory entry index (`by_id` map + leaf pointer).
-//!   - Deferred file creation: the file is not written until the first
-//!     assistant message persists. Until that point, all entries are
-//!     buffered in memory.
-//!   - Append semantics: once flushed, every completed entry is written
-//!     and synced to disk immediately.
-//!   - Crash recovery: on open, the file is parsed line-by-line; the first
-//!     line that fails to parse causes everything from that line onward to
-//!     be truncated from the file.
-//!   - One-time format migration when a future version reads a v1 file
-//!     (currently a no-op; the hook is in place).
-//!   - Rebuilding a `Conversation` from the entry tree, plus determining
-//!     the active provider/model.
-//!
-//! The library-vs-CLI boundary: callers pass an absolute path to the
-//! per-cwd sessions directory. We compute the per-session filename
-//! ourselves (`<uuidv7>.jsonl`) and lazily mkdir the directory on the
-//! first flush. The CLI owns XDG resolution, encoded-cwd grouping, and
-//! the `--resume` flag plumbing.
-
-const std = @import("std");
-const Allocator = std.mem.Allocator;
-const Io = std.Io;
-
-const session_mod = @import("session.zig");
-const conversation_mod = @import("conversation.zig");
-const session_store_mod = @import("session_store.zig");
-
-pub const SessionHeader = session_mod.SessionHeader;
-pub const SessionEntry = session_mod.SessionEntry;
-pub const MessageEntry = session_mod.MessageEntry;
-pub const DiskMessage = session_mod.DiskMessage;
-pub const DiskMessageRole = session_mod.DiskMessageRole;
-pub const DiskSystemMode = session_mod.DiskSystemMode;
-pub const DiskContentBlock = session_mod.DiskContentBlock;
-pub const Usage = session_mod.Usage;
-pub const CURRENT_VERSION = session_mod.CURRENT_VERSION;
-
-// =============================================================================
-// IDs and timestamps
-// =============================================================================
-
-/// Generate a UUIDv7 (RFC 9562 §5.7). Returns a 36-character canonical
-/// hex string with hyphens. Caller owns.
-///
-/// Layout:
-///   - 48 bits: unix_ts_ms (big-endian)
-///   - 4 bits: version (7)
-///   - 12 bits: random
-///   - 2 bits: variant (10)
-///   - 62 bits: random
-pub fn newUuidV7(allocator: Allocator, io: Io) ![]u8 {
-    const ts = Io.Timestamp.now(io, .real);
-    const now_ms: u64 = @intCast(@max(ts.toMilliseconds(), 0));
-
-    var rand_bytes: [10]u8 = undefined;
-    io.random(&rand_bytes);
-
-    var b: [16]u8 = undefined;
-    // Timestamp (48 bits, big-endian).
-    b[0] = @intCast((now_ms >> 40) & 0xFF);
-    b[1] = @intCast((now_ms >> 32) & 0xFF);
-    b[2] = @intCast((now_ms >> 24) & 0xFF);
-    b[3] = @intCast((now_ms >> 16) & 0xFF);
-    b[4] = @intCast((now_ms >> 8) & 0xFF);
-    b[5] = @intCast(now_ms & 0xFF);
-    // Version (4 high bits = 0x7) + 12 bits random.
-    b[6] = 0x70 | (rand_bytes[0] & 0x0F);
-    b[7] = rand_bytes[1];
-    // Variant (2 high bits = 10) + 62 bits random.
-    b[8] = 0x80 | (rand_bytes[2] & 0x3F);
-    b[9] = rand_bytes[3];
-    b[10] = rand_bytes[4];
-    b[11] = rand_bytes[5];
-    b[12] = rand_bytes[6];
-    b[13] = rand_bytes[7];
-    b[14] = rand_bytes[8];
-    b[15] = rand_bytes[9];
-
-    return try std.fmt.allocPrint(
-        allocator,
-        "{x:0>2}{x:0>2}{x:0>2}{x:0>2}-{x:0>2}{x:0>2}-{x:0>2}{x:0>2}-{x:0>2}{x:0>2}-{x:0>2}{x:0>2}{x:0>2}{x:0>2}{x:0>2}{x:0>2}",
-        .{ b[0], b[1], b[2], b[3], b[4], b[5], b[6], b[7], b[8], b[9], b[10], b[11], b[12], b[13], b[14], b[15] },
-    );
-}
-
-/// Generate a fresh 8-character hex entry id. Caller owns.
-fn newEntryIdInto(buf: []u8, io: Io) void {
-    std.debug.assert(buf.len == 8);
-    var bytes: [4]u8 = undefined;
-    io.random(&bytes);
-    _ = std.fmt.bufPrint(buf, "{x:0>2}{x:0>2}{x:0>2}{x:0>2}", .{ bytes[0], bytes[1], bytes[2], bytes[3] }) catch unreachable;
-}
-
-/// Format `now` as an ISO 8601 UTC string with millisecond precision.
-/// Example: `2026-04-25T17:40:15.990Z`. Caller owns.
-pub fn isoTimestamp(allocator: Allocator, io: Io) ![]u8 {
-    const ts = Io.Timestamp.now(io, .real);
-    const ms_total: i64 = ts.toMilliseconds();
-    const seconds_total: i64 = @divTrunc(ms_total, 1000);
-    const ms: u64 = @intCast(@mod(ms_total, 1000));
-
-    const epoch_secs = std.time.epoch.EpochSeconds{ .secs = @intCast(seconds_total) };
-    const epoch_day = epoch_secs.getEpochDay();
-    const day_secs = epoch_secs.getDaySeconds();
-    const year_day = epoch_day.calculateYearDay();
-    const month_day = year_day.calculateMonthDay();
-
-    return try std.fmt.allocPrint(
-        allocator,
-        "{d:0>4}-{d:0>2}-{d:0>2}T{d:0>2}:{d:0>2}:{d:0>2}.{d:0>3}Z",
-        .{
-            @as(u32, year_day.year),
-            month_day.month.numeric(),
-            @as(u32, month_day.day_index) + 1,
-            day_secs.getHoursIntoDay(),
-            day_secs.getMinutesIntoHour(),
-            day_secs.getSecondsIntoMinute(),
-            ms,
-        },
-    );
-}
-
-// =============================================================================
-// SessionInfo (listing)
-// =============================================================================
-
-pub const SessionInfo = struct {
-    path: []u8,
-    id: []u8,
-    cwd: []u8,
-    created: []u8, // ISO 8601 from header timestamp
-    modified: []u8, // ISO 8601 from last user/assistant entry, falling back to header, then file mtime
-    message_count: usize,
-
-    pub fn deinit(self: SessionInfo, alloc: Allocator) void {
-        alloc.free(self.path);
-        alloc.free(self.id);
-        alloc.free(self.cwd);
-        alloc.free(self.created);
-        alloc.free(self.modified);
-    }
-};
-
-pub fn freeSessionInfos(alloc: Allocator, infos: []SessionInfo) void {
-    for (infos) |info| info.deinit(alloc);
-    alloc.free(infos);
-}
-
-// =============================================================================
-// SessionManager
-// =============================================================================
-
-pub const Error = error{
-    NoSessionsFound,
-    AmbiguousSessionId,
-    SessionNotFound,
-    InvalidSessionFile,
-} || Allocator.Error || Io.Cancelable;
-
-pub const SessionManager = struct {
-    allocator: Allocator,
-    io: Io,
-
-    /// Absolute path to the per-cwd sessions directory. Lazily created.
-    session_dir: []u8,
-    /// Absolute path to the file we *will* write to (computed at init).
-    /// May not yet exist on disk if `flushed = false`.
-    session_file: []u8,
-
-    /// Header. Allocated at init for new sessions; reloaded from the file
-    /// on resume.
-    header: SessionHeader,
-
-    /// Entries indexed in insertion order. The first entry's `parent_id`
-    /// is null; each subsequent entry's `parent_id` points to its parent
-    /// (currently always the previous entry).
-    entries: std.ArrayList(SessionEntry),
-    /// id → entry index in `entries`. Used both for parent-id lookups
-    /// and for collision detection in `newEntryId`.
-    by_id: std.StringHashMap(usize),
-    /// id of the most recently appended entry, or null if no entries yet.
-    /// Borrowed from the entry; do not free.
-    leaf_id: ?[]const u8,
-
-    /// True once the file exists on disk. False during the "buffered"
-    /// pre-assistant phase. See module-level docs.
-    flushed: bool,
-    /// Number of bytes written to `session_file` so far. Used as the
-    /// offset for the next positional write. Only meaningful when
-    /// `flushed = true`.
-    written_bytes: u64,
-
-    // ---------- Construction ----------
-
-    /// Create a new session in memory. Allocates a UUIDv7, computes the
-    /// file path, but does NOT touch the filesystem. The file is created
-    /// on the first assistant-message flush.
-    ///
-    /// `session_dir` is duplicated; the caller retains ownership of the
-    /// passed slice.
-    pub fn init(
-        allocator: Allocator,
-        io: Io,
-        session_dir: []const u8,
-        cwd: []const u8,
-    ) !SessionManager {
-        const dir = try allocator.dupe(u8, session_dir);
-        errdefer allocator.free(dir);
-
-        const id = try newUuidV7(allocator, io);
-        errdefer allocator.free(id);
-
-        const timestamp = try isoTimestamp(allocator, io);
-        errdefer allocator.free(timestamp);
-
-        const cwd_copy = try allocator.dupe(u8, cwd);
-        errdefer allocator.free(cwd_copy);
-
-        const filename = try std.fmt.allocPrint(allocator, "{s}.jsonl", .{id});
-        defer allocator.free(filename);
-        const file_path = try std.fs.path.join(allocator, &.{ dir, filename });
-        errdefer allocator.free(file_path);
-
-        return .{
-            .allocator = allocator,
-            .io = io,
-            .session_dir = dir,
-            .session_file = file_path,
-            .header = .{
-                .version = CURRENT_VERSION,
-                .id = id,
-                .timestamp = timestamp,
-                .cwd = cwd_copy,
-            },
-            .entries = .empty,
-            .by_id = std.StringHashMap(usize).init(allocator),
-            .leaf_id = null,
-            .flushed = false,
-            .written_bytes = 0,
-        };
-    }
-
-    /// Open and replay an existing session file. Truncates from the first
-    /// corrupted line. Runs format migration if needed and rewrites the
-    /// file once.
-    pub fn open(
-        allocator: Allocator,
-        io: Io,
-        file_path: []const u8,
-    ) !SessionManager {
-        const path_copy = try allocator.dupe(u8, file_path);
-        errdefer allocator.free(path_copy);
-
-        // The session dir is the file's parent directory.
-        const dir_path = std.fs.path.dirname(path_copy) orelse ".";
-        const dir = try allocator.dupe(u8, dir_path);
-        errdefer allocator.free(dir);
-
-        const bytes = try readWholeFile(allocator, io, path_copy);
-        defer allocator.free(bytes);
-
-        // Walk line-by-line. The first failure causes a truncation back to
-        // the start of that line.
-        var entries: std.ArrayList(SessionEntry) = .empty;
-        errdefer {
-            for (entries.items) |e| e.deinit(allocator);
-            entries.deinit(allocator);
-        }
-        var by_id = std.StringHashMap(usize).init(allocator);
-        errdefer by_id.deinit();
-
-        var header_opt: ?SessionHeader = null;
-        errdefer if (header_opt) |h| h.deinit(allocator);
-
-        var cursor: usize = 0;
-        var valid_bytes: u64 = 0; // length of the file prefix that parses cleanly
-        var saw_corruption: bool = false;
-
-        while (cursor < bytes.len) {
-            // Find the next newline (or EOF).
-            const rest = bytes[cursor..];
-            const nl_rel = std.mem.indexOfScalar(u8, rest, '\n');
-            const line_end_excl: usize = if (nl_rel) |n| cursor + n else bytes.len;
-            const line = bytes[cursor..line_end_excl];
-            const next_cursor: usize = if (nl_rel != null) line_end_excl + 1 else bytes.len;
-
-            // Allow blank lines silently (just whitespace), but a non-empty
-            // trimmed line that won't parse triggers truncation.
-            const trimmed = std.mem.trim(u8, line, " \t\r");
-            if (trimmed.len == 0) {
-                if (nl_rel == null) break;
-                cursor = next_cursor;
-                valid_bytes = cursor;
-                continue;
-            }
-
-            // If the final line has no trailing newline AND we hit EOF, it
-            // is presumed truncated mid-write. Treat as corruption.
-            if (nl_rel == null) {
-                saw_corruption = true;
-                break;
-            }
-
-            const fe = session_mod.parseLine(allocator, line) catch {
-                saw_corruption = true;
-                break;
-            };
-
-            switch (fe) {
-                .header => |h| {
-                    if (header_opt != null) {
-                        // Two headers — treat as corruption from this line on.
-                        h.deinit(allocator);
-                        saw_corruption = true;
-                        break;
-                    }
-                    if (entries.items.len != 0) {
-                        // Header arrived after entries — malformed.
-                        h.deinit(allocator);
-                        saw_corruption = true;
-                        break;
-                    }
-                    header_opt = h;
-                },
-                .entry => |e| {
-                    const idx = entries.items.len;
-                    entries.append(allocator, e) catch |err| {
-                        e.deinit(allocator);
-                        return err;
-                    };
-                    by_id.put(e.base().id, idx) catch |err| {
-                        // Rolling back the append is awkward; in practice
-                        // OOM here is fatal anyway.
-                        return err;
-                    };
-                },
-            }
-
-            cursor = next_cursor;
-            valid_bytes = cursor;
-        }
-
-        // No header at all — refuse to load.
-        const header = header_opt orelse return error.InvalidSessionFile;
-
-        // Truncate the file if anything beyond `valid_bytes` is corrupt.
-        if (saw_corruption and valid_bytes < bytes.len) {
-            try truncateFileTo(io, path_copy, valid_bytes);
-        }
-
-        var migrated_header = header;
-        var did_migrate = migrate(allocator, &migrated_header, &entries);
-        if (elideDanglingToolUses(allocator, &entries)) {
-            did_migrate = true;
-        }
-        // We didn't reassign by_id during migration; rebuild if needed.
-        if (did_migrate) {
-            by_id.clearRetainingCapacity();
-            for (entries.items, 0..) |e, i| {
-                try by_id.put(e.base().id, i);
-            }
-            try rewriteFile(allocator, io, path_copy, migrated_header, entries.items);
-        }
-
-        const leaf_id: ?[]const u8 = if (entries.items.len > 0)
-            entries.items[entries.items.len - 1].base().id
-        else
-            null;
-
-        // Compute final file length on disk so future appends use the
-        // correct offset.
-        const stat = try statFileForLength(io, path_copy);
-
-        return .{
-            .allocator = allocator,
-            .io = io,
-            .session_dir = dir,
-            .session_file = path_copy,
-            .header = migrated_header,
-            .entries = entries,
-            .by_id = by_id,
-            .leaf_id = leaf_id,
-            .flushed = true,
-            .written_bytes = stat,
-        };
-    }
-
-    pub fn deinit(self: *SessionManager) void {
-        self.header.deinit(self.allocator);
-        for (self.entries.items) |e| e.deinit(self.allocator);
-        self.entries.deinit(self.allocator);
-        self.by_id.deinit();
-        self.allocator.free(self.session_dir);
-        self.allocator.free(self.session_file);
-    }
-
-    // ---------- Accessors ----------
-
-    pub fn getCwd(self: *const SessionManager) []const u8 {
-        return self.header.cwd;
-    }
-
-    pub fn getSessionId(self: *const SessionManager) []const u8 {
-        return self.header.id;
-    }
-
-    pub fn getSessionFile(self: *const SessionManager) []const u8 {
-        return self.session_file;
-    }
-
-    pub fn getSessionDir(self: *const SessionManager) []const u8 {
-        return self.session_dir;
-    }
-
-    pub fn getLeafId(self: *const SessionManager) ?[]const u8 {
-        return self.leaf_id;
-    }
-
-    pub fn getEntry(self: *const SessionManager, id: []const u8) ?*const SessionEntry {
-        const idx = self.by_id.get(id) orelse return null;
-        return &self.entries.items[idx];
-    }
-
-    pub fn getEntries(self: *const SessionManager) []const SessionEntry {
-        return self.entries.items;
-    }
-
-    pub fn isFlushed(self: *const SessionManager) bool {
-        return self.flushed;
-    }
-
-    // ---------- Active model resolution ----------
-
-    /// Determine the active provider/model by walking entries leaf→root
-    /// and finding the last user-message entry with provider/model
-    /// stamped. Returns null only when no user message has been appended
-    /// yet, which is only reachable on a freshly-`init`'d session before
-    /// the first user prompt (and therefore before any disk flush).
-    ///
-    /// Returns borrowed slices owned by the manager; do not free.
-    pub fn activeModel(self: *const SessionManager) ?struct { provider: []const u8, model: []const u8 } {
-        var i = self.entries.items.len;
-        while (i > 0) : (i -= 1) {
-            const e = self.entries.items[i - 1];
-            switch (e) {
-                .message => |m| {
-                    if (m.message.role == .user) {
-                        if (m.provider) |p| {
-                            if (m.model) |mo| {
-                                return .{ .provider = p, .model = mo };
-                            }
-                        }
-                    }
-                },
-            }
-        }
-        return null;
-    }
-
-    // ---------- Appending ----------
-
-    /// Append a message entry. `msg` is consumed (ownership transferred)
-    /// regardless of success — on error, the message is deinit'd before
-    /// the error is returned.
-    ///
-    /// If `flushed`: writes the new line immediately.
-    /// If not flushed and `msg.role == .assistant`: writes the header +
-    /// all buffered entries + the new entry, then sets `flushed`.
-    /// Otherwise: buffers in memory only.
-    pub fn appendMessage(
-        self: *SessionManager,
-        msg: DiskMessage,
-        // Top-level stamps on the entry (vs. inside the message).
-        // Stamped only on user messages.
-        provider: ?[]const u8,
-        model: ?[]const u8,
-    ) ![]const u8 {
-        // Build the entry up-front, taking ownership of the inputs.
-        var msg_local = msg;
-        errdefer msg_local.deinit(self.allocator);
-
-        const id_buf = try self.newEntryId();
-        errdefer self.allocator.free(id_buf);
-
-        const timestamp = try isoTimestamp(self.allocator, self.io);
-        errdefer self.allocator.free(timestamp);
-
-        const parent_id_copy: ?[]const u8 = if (self.leaf_id) |l| try self.allocator.dupe(u8, l) else null;
-        errdefer if (parent_id_copy) |p| self.allocator.free(p);
-
-        const provider_copy: ?[]const u8 = if (provider) |p| try self.allocator.dupe(u8, p) else null;
-        errdefer if (provider_copy) |p| self.allocator.free(p);
-
-        const model_copy: ?[]const u8 = if (model) |m| try self.allocator.dupe(u8, m) else null;
-        errdefer if (model_copy) |m| self.allocator.free(m);
-
-        const entry: SessionEntry = .{ .message = .{
-            .base = .{ .id = id_buf, .parent_id = parent_id_copy, .timestamp = timestamp },
-            .provider = provider_copy,
-            .model = model_copy,
-            .message = msg_local,
-        } };
-
-        // The entry now owns msg_local + id_buf + timestamp + parent_id_copy +
-        // provider/model copies. Cancel the errdefers individually.
-        // (Zig's errdefer behavior: they only run on error returns; pushing the
-        // entry into entries.items before any further fallible step means an
-        // error in by_id.put() would double-free. Instead, do the put first
-        // against a not-yet-stored id.)
-
-        const idx = self.entries.items.len;
-
-        // Ensure capacity before touching anything.
-        try self.entries.ensureUnusedCapacity(self.allocator, 1);
-        try self.by_id.ensureUnusedCapacity(1);
-
-        // Persist BEFORE inserting into the in-memory structures, so that on
-        // I/O failure we don't have a dangling in-memory entry the caller
-        // thinks was saved. (Failure leaves the file unchanged for an
-        // unflushed session, and unchanged-except-for-EOF for a flushed one.)
-        const is_assistant = entry.message.message.role == .assistant;
-        if (self.flushed) {
-            try self.persistEntry(entry);
-        } else if (is_assistant) {
-            try self.flushBuffered(entry);
-        }
-        // If not flushed and not assistant: nothing to do; the entry will be
-        // flushed alongside the eventual first assistant entry.
-
-        // Now insert into in-memory structures. All allocations are kept.
-        self.entries.appendAssumeCapacity(entry);
-        self.by_id.putAssumeCapacity(entry.base().id, idx);
-        self.leaf_id = entry.base().id;
-        return entry.base().id;
-    }
-
-    /// Returns a freshly allocated 8-character hex id, guaranteed not to
-    /// collide with any existing entry id in this session.
-    fn newEntryId(self: *SessionManager) ![]u8 {
-        const max_tries = 100;
-        var i: usize = 0;
-        while (i < max_tries) : (i += 1) {
-            const buf = try self.allocator.alloc(u8, 8);
-            errdefer self.allocator.free(buf);
-            newEntryIdInto(buf[0..8], self.io);
-            if (!self.by_id.contains(buf)) {
-                return buf;
-            }
-            self.allocator.free(buf);
-        }
-        // Fall back to a UUID prefix if 100 retries all collided. With 4
-        // random bytes per id and a session with <<2^16 entries, the
-        // probability of getting here is effectively zero, but we want a
-        // hard guarantee.
-        const long = try newUuidV7(self.allocator, self.io);
-        defer self.allocator.free(long);
-        const buf = try self.allocator.alloc(u8, 8);
-        @memcpy(buf, long[0..8]);
-        return buf;
-    }
-
-    // ---------- Persistence ----------
-
-    /// Write the header + all currently-buffered entries + `new_entries`
-    /// to the file as a single batch. Creates the directory and file.
-    fn flushBufferedMany(self: *SessionManager, new_entries: []const SessionEntry) !void {
-        try mkdirP(self.io, self.session_dir);
-
-        const file = try Io.Dir.cwd().createFile(self.io, self.session_file, .{
-            .truncate = true,
-            .read = false,
-        });
-        defer file.close(self.io);
-
-        var offset: u64 = 0;
-        const header_line = try session_mod.serializeHeader(self.allocator, self.header);
-        defer self.allocator.free(header_line);
-        try file.writePositionalAll(self.io, header_line, offset);
-        offset += header_line.len;
-        try file.writePositionalAll(self.io, "\n", offset);
-        offset += 1;
-
-        for (self.entries.items) |e| {
-            const line = try session_mod.serializeEntry(self.allocator, e);
-            defer self.allocator.free(line);
-            try file.writePositionalAll(self.io, line, offset);
-            offset += line.len;
-            try file.writePositionalAll(self.io, "\n", offset);
-            offset += 1;
-        }
-
-        for (new_entries) |entry| {
-            const line = try session_mod.serializeEntry(self.allocator, entry);
-            defer self.allocator.free(line);
-            try file.writePositionalAll(self.io, line, offset);
-            offset += line.len;
-            try file.writePositionalAll(self.io, "\n", offset);
-            offset += 1;
-        }
-
-        file.sync(self.io) catch {};
-        self.flushed = true;
-        self.written_bytes = offset;
-    }
-
-    fn flushBuffered(self: *SessionManager, final_entry: SessionEntry) !void {
-        try self.flushBufferedMany(&.{final_entry});
-    }
-
-    /// Append a single line for `entry` to the open session file. Caller
-    /// must have already verified `flushed`.
-    fn persistEntry(self: *SessionManager, entry: SessionEntry) !void {
-        try self.persistEntries(&.{entry});
-    }
-
-    pub fn appendMessagesAtomic(
-        self: *SessionManager,
-        messages: []DiskMessage,
-        providers: []const ?[]const u8,
-        models: []const ?[]const u8,
-    ) !void {
-        std.debug.assert(messages.len == providers.len);
-        std.debug.assert(messages.len == models.len);
-        if (messages.len == 0) return;
-
-        const base_len = self.entries.items.len;
-        try self.entries.ensureUnusedCapacity(self.allocator, messages.len);
-        try self.by_id.ensureUnusedCapacity(@intCast(messages.len));
-
-        var entries = try self.allocator.alloc(SessionEntry, messages.len);
-        defer self.allocator.free(entries);
-        var built: usize = 0;
-        errdefer {
-            for (entries[0..built]) |*e| e.deinit(self.allocator);
-        }
-
-        var prev_leaf = self.leaf_id;
-        for (messages, 0..) |msg, i| {
-            const msg_local = msg;
-            const id_buf = try self.newEntryId();
-            errdefer self.allocator.free(id_buf);
-            const timestamp = try isoTimestamp(self.allocator, self.io);
-            errdefer self.allocator.free(timestamp);
-            const parent_id_copy: ?[]const u8 = if (prev_leaf) |l| try self.allocator.dupe(u8, l) else null;
-            errdefer if (parent_id_copy) |p| self.allocator.free(p);
-            const provider_copy: ?[]const u8 = if (providers[i]) |p| try self.allocator.dupe(u8, p) else null;
-            errdefer if (provider_copy) |p| self.allocator.free(p);
-            const model_copy: ?[]const u8 = if (models[i]) |m| try self.allocator.dupe(u8, m) else null;
-            errdefer if (model_copy) |m| self.allocator.free(m);
-            entries[i] = .{ .message = .{
-                .base = .{ .id = id_buf, .parent_id = parent_id_copy, .timestamp = timestamp },
-                .provider = provider_copy,
-                .model = model_copy,
-                .message = msg_local,
-            } };
-            built += 1;
-            prev_leaf = entries[i].base().id;
-        }
-
-        if (self.flushed) {
-            try self.persistEntries(entries);
-        } else {
-            try self.flushBufferedMany(entries);
-        }
-
-        for (entries, 0..) |entry, i| {
-            self.entries.appendAssumeCapacity(entry);
-            self.by_id.putAssumeCapacity(entry.base().id, base_len + i);
-        }
-        self.leaf_id = entries[entries.len - 1].base().id;
-        built = 0;
-    }
-
-    fn persistEntries(self: *SessionManager, entries: []const SessionEntry) !void {
-        const file = try Io.Dir.cwd().openFile(self.io, self.session_file, .{
-            .mode = .write_only,
-        });
-        defer file.close(self.io);
-
-        var offset = self.written_bytes;
-        for (entries) |entry| {
-            const line = try session_mod.serializeEntry(self.allocator, entry);
-            defer self.allocator.free(line);
-            try file.writePositionalAll(self.io, line, offset);
-            offset += line.len;
-            try file.writePositionalAll(self.io, "\n", offset);
-            offset += 1;
-        }
-        file.sync(self.io) catch {};
-        self.written_bytes = offset;
-    }
-
-    // =============================================================================
-    // Conversation rebuild
-    // =============================================================================
-
-    /// Build a fresh `Conversation` from the entry log. Caller owns the
-    /// returned conversation (call `deinit`).
-    pub fn rebuildConversation(self: *const SessionManager) !conversation_mod.Conversation {
-        var conv = conversation_mod.Conversation.init(self.allocator);
-        errdefer conv.deinit();
-
-        for (self.entries.items) |entry| {
-            switch (entry) {
-                .message => |me| try appendMessageToConv(&conv, self.allocator, me.message),
-            }
-        }
-        return conv;
-    }
-
-    // =============================================================================
-    // SessionStore interface
-    // =============================================================================
-
-    /// Reconstruct a linear `Conversation` plus an optional dangling
-    /// trailing user prompt (a user entry with no following assistant —
-    /// e.g. a crash/quit right after submission). The returned conversation
-    /// **excludes** that dangling user turn; its text is returned as
-    /// `dangling_user` (owned by `alloc`) so a resumed agent never
-    /// auto-sends it.
-    pub fn loadConversation(
-        self: *const SessionManager,
-        alloc: Allocator,
-    ) !session_store_mod.LoadedSession {
-        // Detect a dangling trailing user entry: the last message entry is
-        // a user message and nothing follows it. (Entries are linear; the
-        // last entry is the leaf.)
-        const items = self.entries.items;
-        var dangling: ?[]const u8 = null;
-        var stop_at: usize = items.len;
-        if (items.len > 0) {
-            const last = items[items.len - 1];
-            switch (last) {
-                .message => |me| {
-                    if (me.message.role == .user) {
-                        dangling = try extractUserText(alloc, me.message);
-                        // Only treat it as dangling (and exclude it) when we
-                        // could actually recover prompt text; otherwise keep
-                        // it in the conversation rather than silently drop.
-                        if (dangling != null) stop_at = items.len - 1;
-                    }
-                },
-            }
-        }
-        errdefer if (dangling) |d| alloc.free(d);
-
-        var conv = conversation_mod.Conversation.init(alloc);
-        errdefer conv.deinit();
-        for (items[0..stop_at]) |entry| {
-            switch (entry) {
-                .message => |me| try appendMessageToConv(&conv, alloc, me.message),
-            }
-        }
-
-        return .{ .conversation = conv, .dangling_user = dangling };
-    }
-
-    fn appendMessagesVT(
-        ctx: *anyopaque,
-        messages: []session_store_mod.DiskMessage,
-        providers: []const ?[]const u8,
-        models: []const ?[]const u8,
-    ) anyerror!void {
-        const self: *SessionManager = @ptrCast(@alignCast(ctx));
-        try self.appendMessagesAtomic(messages, providers, models);
-    }
-
-    fn loadConversationVT(
-        ctx: *anyopaque,
-        alloc: Allocator,
-    ) anyerror!session_store_mod.LoadedSession {
-        const self: *const SessionManager = @ptrCast(@alignCast(ctx));
-        return self.loadConversation(alloc);
-    }
-
-    fn sessionIdVT(ctx: *anyopaque) []const u8 {
-        const self: *const SessionManager = @ptrCast(@alignCast(ctx));
-        return self.getSessionId();
-    }
-
-    fn activeModelVT(ctx: *anyopaque) ?session_store_mod.ActiveModel {
-        const self: *const SessionManager = @ptrCast(@alignCast(ctx));
-        const am = self.activeModel() orelse return null;
-        return .{ .provider = am.provider, .model = am.model };
-    }
-
-    const store_vtable: session_store_mod.SessionStore.VTable = .{
-        .appendMessages = appendMessagesVT,
-        .loadConversation = loadConversationVT,
-        .sessionId = sessionIdVT,
-        .activeModel = activeModelVT,
-    };
-
-    /// Wrap this concrete manager as a neutral `SessionStore`. The returned
-    /// store borrows `self`; `self` must outlive it.
-    pub fn store(self: *SessionManager) session_store_mod.SessionStore {
-        return .{ .ptr = self, .vtable = &store_vtable };
-    }
-};
-
-/// Best-effort extraction of plain prompt text from a user `DiskMessage`.
-/// Returns null if the message carries no plain text block (e.g. it is a
-/// tool-result-only user message, which is never a "dangling prompt").
-/// Caller owns the returned slice.
-fn extractUserText(alloc: Allocator, msg: DiskMessage) !?[]const u8 {
-    for (msg.content) |block| {
-        if (block == .text) {
-            return try alloc.dupe(u8, block.text.text);
-        }
-    }
-    return null;
-}
-
-fn appendMessageToConv(
-    conv: *conversation_mod.Conversation,
-    allocator: Allocator,
-    disk_msg: DiskMessage,
-) !void {
-    var content: std.ArrayList(conversation_mod.ContentBlock) = .empty;
-    errdefer {
-        for (content.items) |*b| {
-            var mut = b.*;
-            mut.deinit(allocator);
-        }
-        content.deinit(allocator);
-    }
-    try content.ensureTotalCapacity(allocator, disk_msg.content.len);
-    const sys_mode: conversation_mod.SystemMode = switch (disk_msg.mode) {
-        .append => .append,
-        .replace => .replace,
-    };
-    for (disk_msg.content) |db| {
-        var block = try session_mod.diskContentBlockToInternal(allocator, db);
-        // System-role text blocks become `.System` blocks carrying the
-        // message's recorded mode, so the append/replace derivation works
-        // on the rebuilt conversation exactly as it did when written.
-        if (disk_msg.role == .system and block == .Text) {
-            const tb = block.Text;
-            block = .{ .System = .{ .text = tb, .mode = sys_mode } };
-        }
-        content.appendAssumeCapacity(block);
-    }
-    const role: conversation_mod.MessageRole = switch (disk_msg.role) {
-        .system => .system,
-        .user => .user,
-        .assistant => .assistant,
-    };
-    // Carry the recorded usage forward so compaction can size the retention
-    // window after a session is reopened (it's null for user/system).
-    try conv.messages.append(allocator, .{
-        .role = role,
-        .content = content,
-        .usage = disk_msg.usage,
-    });
-}
-
-// =============================================================================
-// Migration
-// =============================================================================
-
-/// Future format migrations land here. Returns true if anything changed
-/// (which triggers a one-time file rewrite).
-fn migrate(
-    allocator: Allocator,
-    header: *SessionHeader,
-    entries: *std.ArrayList(SessionEntry),
-) bool {
-    _ = allocator;
-    _ = entries;
-    if (header.version >= CURRENT_VERSION) return false;
-    // No earlier versions exist yet. When v2 lands, transform v1 entries
-    // here and bump `header.version`.
-    return false;
-}
-
-fn elideDanglingToolUses(allocator: Allocator, entries: *std.ArrayList(SessionEntry)) bool {
-    var needed: std.StringHashMap(void) = .init(allocator);
-    defer needed.deinit();
-    var changed = false;
-
-    var i = entries.items.len;
-    while (i > 0) {
-        i -= 1;
-        const entry = &entries.items[i];
-        if (entry.* != .message) continue;
-        const msg = &entry.message.message;
-
-        if (msg.role == .user) {
-            for (msg.content) |block| {
-                if (block == .tool_result) {
-                    needed.put(block.tool_result.tool_use_id, {}) catch {};
-                }
-            }
-            continue;
-        }
-
-        if (msg.role != .assistant) continue;
-        var kept: std.ArrayList(DiskContentBlock) = .empty;
-        defer kept.deinit(allocator);
-        var removed = false;
-        for (msg.content) |block| {
-            if (block == .tool_use and !needed.contains(block.tool_use.id)) {
-                block.deinit(allocator);
-                removed = true;
-                continue;
-            }
-            kept.append(allocator, block) catch unreachable;
-        }
-        if (!removed) continue;
-        allocator.free(msg.content);
-        msg.content = kept.toOwnedSlice(allocator) catch unreachable;
-        changed = true;
-    }
-    return changed;
-}
-
-// =============================================================================
-// File utilities
-// =============================================================================
-
-fn readWholeFile(allocator: Allocator, io: Io, path: []const u8) ![]u8 {
-    const file = Io.Dir.cwd().openFile(io, path, .{ .mode = .read_only }) catch |err| switch (err) {
-        error.FileNotFound => return error.InvalidSessionFile,
-        else => return err,
-    };
-    defer file.close(io);
-
-    const len = file.length(io) catch {
-        // Fall back to a streaming read of a reasonable upper bound.
-        // Sessions over ~10 MB are out of scope for phase 4.
-        var list: std.ArrayList(u8) = .empty;
-        defer list.deinit(allocator);
-        var chunk: [4096]u8 = undefined;
-        while (true) {
-            const n = file.readStreaming(io, &.{&chunk}) catch break;
-            if (n == 0) break;
-            try list.appendSlice(allocator, chunk[0..n]);
-        }
-        return try list.toOwnedSlice(allocator);
-    };
-
-    const buf = try allocator.alloc(u8, @intCast(len));
-    errdefer allocator.free(buf);
-    _ = try file.readPositionalAll(io, buf, 0);
-    return buf;
-}
-
-fn statFileForLength(io: Io, path: []const u8) !u64 {
-    const file = try Io.Dir.cwd().openFile(io, path, .{ .mode = .read_only });
-    defer file.close(io);
-    return try file.length(io);
-}
-
-fn truncateFileTo(io: Io, path: []const u8, new_length: u64) !void {
-    const file = try Io.Dir.cwd().openFile(io, path, .{ .mode = .write_only });
-    defer file.close(io);
-    try file.setLength(io, new_length);
-    file.sync(io) catch {};
-}
-
-/// Write a fresh file containing `header` followed by `entries`. Truncates
-/// any existing content. Used after a migration rewrites the format.
-fn rewriteFile(
-    allocator: Allocator,
-    io: Io,
-    path: []const u8,
-    header: SessionHeader,
-    entries: []const SessionEntry,
-) !void {
-    const file = try Io.Dir.cwd().createFile(io, path, .{
-        .truncate = true,
-        .read = false,
-    });
-    defer file.close(io);
-
-    var offset: u64 = 0;
-    const header_line = try session_mod.serializeHeader(allocator, header);
-    defer allocator.free(header_line);
-    try file.writePositionalAll(io, header_line, offset);
-    offset += header_line.len;
-    try file.writePositionalAll(io, "\n", offset);
-    offset += 1;
-    for (entries) |e| {
-        const line = try session_mod.serializeEntry(allocator, e);
-        defer allocator.free(line);
-        try file.writePositionalAll(io, line, offset);
-        offset += line.len;
-        try file.writePositionalAll(io, "\n", offset);
-        offset += 1;
-    }
-    file.sync(io) catch {};
-}
-
-fn mkdirP(io: Io, path: []const u8) !void {
-    Io.Dir.cwd().createDirPath(io, path) catch |err| switch (err) {
-        error.PathAlreadyExists => {},
-        else => return err,
-    };
-}
-
-// =============================================================================
-// Listing
-// =============================================================================
-
-/// List sessions in `session_dir`. Returns a slice of `SessionInfo`s
-/// sorted by `modified` descending (most recent first). Caller owns the
-/// slice and each `SessionInfo`.
-///
-/// If the directory does not exist, returns an empty slice (no error).
-///
-/// If `on_progress` is non-null, it is invoked after each file is parsed.
-pub fn listSessions(
-    allocator: Allocator,
-    io: Io,
-    session_dir: []const u8,
-    on_progress: ?*const fn (loaded: usize, total: usize) void,
-) ![]SessionInfo {
-    var dir = Io.Dir.cwd().openDir(io, session_dir, .{}) catch |err| switch (err) {
-        error.FileNotFound => return try allocator.alloc(SessionInfo, 0),
-        else => return err,
-    };
-    defer dir.close(io);
-
-    var names: std.ArrayList([]u8) = .empty;
-    defer {
-        for (names.items) |n| allocator.free(n);
-        names.deinit(allocator);
-    }
-
-    var it = dir.iterate();
-    while (try it.next(io)) |entry| {
-        if (entry.kind != .file) continue;
-        if (!std.mem.endsWith(u8, entry.name, ".jsonl")) continue;
-        const copy = try allocator.dupe(u8, entry.name);
-        errdefer allocator.free(copy);
-        try names.append(allocator, copy);
-    }
-
-    var infos: std.ArrayList(SessionInfo) = .empty;
-    errdefer {
-        for (infos.items) |i| i.deinit(allocator);
-        infos.deinit(allocator);
-    }
-    try infos.ensureTotalCapacity(allocator, names.items.len);
-
-    var loaded: usize = 0;
-    for (names.items) |name| {
-        const full = try std.fs.path.join(allocator, &.{ session_dir, name });
-        defer allocator.free(full);
-        const info_opt = buildSessionInfo(allocator, io, full) catch null;
-        if (info_opt) |info| {
-            infos.appendAssumeCapacity(info);
-        }
-        loaded += 1;
-        if (on_progress) |cb| cb(loaded, names.items.len);
-    }
-
-    const slice = try infos.toOwnedSlice(allocator);
-    std.sort.pdq(SessionInfo, slice, {}, sessionInfoNewerFirst);
-    return slice;
-}
-
-fn sessionInfoNewerFirst(_: void, a: SessionInfo, b: SessionInfo) bool {
-    return std.mem.order(u8, a.modified, b.modified) == .gt;
-}
-
-fn buildSessionInfo(
-    allocator: Allocator,
-    io: Io,
-    file_path: []const u8,
-) !?SessionInfo {
-    const bytes = readWholeFile(allocator, io, file_path) catch return null;
-    defer allocator.free(bytes);
-
-    var header_opt: ?SessionHeader = null;
-    defer if (header_opt) |h| h.deinit(allocator);
-
-    var message_count: usize = 0;
-    var last_activity: ?[]u8 = null;
-    defer if (last_activity) |la| allocator.free(la);
-
-    var lines = std.mem.splitScalar(u8, bytes, '\n');
-    while (lines.next()) |line| {
-        const trimmed = std.mem.trim(u8, line, " \t\r");
-        if (trimmed.len == 0) continue;
-        const fe = session_mod.parseLine(allocator, trimmed) catch break;
-        switch (fe) {
-            .header => |h| {
-                if (header_opt != null) {
-                    h.deinit(allocator);
-                } else {
-                    header_opt = h;
-                }
-            },
-            .entry => |e| {
-                defer e.deinit(allocator);
-                switch (e) {
-                    .message => |m| {
-                        if (m.message.role == .user or m.message.role == .assistant) {
-                            message_count += 1;
-                            if (last_activity) |la| allocator.free(la);
-                            last_activity = try allocator.dupe(u8, m.base.timestamp);
-                        }
-                    },
-                }
-            },
-        }
-    }
-
-    const header = header_opt orelse return null;
-    // We will keep header alive through the deinit defer, and dupe its
-    // fields into the result. Cheap, avoids any ownership shuffling.
-
-    const path = try allocator.dupe(u8, file_path);
-    errdefer allocator.free(path);
-    const id = try allocator.dupe(u8, header.id);
-    errdefer allocator.free(id);
-    const cwd = try allocator.dupe(u8, header.cwd);
-    errdefer allocator.free(cwd);
-    const created = try allocator.dupe(u8, header.timestamp);
-    errdefer allocator.free(created);
-    const modified = if (last_activity) |la| blk: {
-        last_activity = null;
-        break :blk la;
-    } else try allocator.dupe(u8, header.timestamp);
-
-    return .{
-        .path = path,
-        .id = id,
-        .cwd = cwd,
-        .created = created,
-        .modified = modified,
-        .message_count = message_count,
-    };
-}
-
-// =============================================================================
-// Recent / resume helpers
-// =============================================================================
-
-/// Find the most recent session file in `session_dir`. Returns null if
-/// none exist. Caller owns the returned path.
-pub fn findMostRecentSession(allocator: Allocator, io: Io, session_dir: []const u8) !?[]u8 {
-    var dir = Io.Dir.cwd().openDir(io, session_dir, .{}) catch |err| switch (err) {
-        error.FileNotFound => return null,
-        else => return err,
-    };
-    defer dir.close(io);
-
-    var best_name: ?[]u8 = null;
-    errdefer if (best_name) |b| allocator.free(b);
-
-    var it = dir.iterate();
-    while (try it.next(io)) |entry| {
-        if (entry.kind != .file) continue;
-        if (!std.mem.endsWith(u8, entry.name, ".jsonl")) continue;
-        if (best_name) |b| {
-            // Lexicographic compare. UUIDv7 filenames sort chronologically.
-            if (std.mem.order(u8, entry.name, b) == .gt) {
-                allocator.free(b);
-                best_name = try allocator.dupe(u8, entry.name);
-            }
-        } else {
-            best_name = try allocator.dupe(u8, entry.name);
-        }
-    }
-
-    const name = best_name orelse return null;
-    defer allocator.free(name);
-    best_name = null;
-    return try std.fs.path.join(allocator, &.{ session_dir, name });
-}
-
-/// Resolve a (possibly abbreviated) session id to a session file path
-/// within `session_dir`. Errors if no match or ambiguous prefix.
-pub fn resolveSessionId(
-    allocator: Allocator,
-    io: Io,
-    session_dir: []const u8,
-    id_or_prefix: []const u8,
-) ![]u8 {
-    var dir = Io.Dir.cwd().openDir(io, session_dir, .{}) catch |err| switch (err) {
-        error.FileNotFound => return error.SessionNotFound,
-        else => return err,
-    };
-    defer dir.close(io);
-
-    var match: ?[]u8 = null;
-    errdefer if (match) |m| allocator.free(m);
-
-    var it = dir.iterate();
-    while (try it.next(io)) |entry| {
-        if (entry.kind != .file) continue;
-        if (!std.mem.endsWith(u8, entry.name, ".jsonl")) continue;
-        // Strip `.jsonl` for the prefix match.
-        const stem = entry.name[0 .. entry.name.len - ".jsonl".len];
-        if (!std.mem.startsWith(u8, stem, id_or_prefix)) continue;
-        if (match != null) return error.AmbiguousSessionId;
-        match = try allocator.dupe(u8, entry.name);
-    }
-
-    const name = match orelse return error.SessionNotFound;
-    defer allocator.free(name);
-    match = null;
-    return try std.fs.path.join(allocator, &.{ session_dir, name });
-}
-
-// =============================================================================
-// Tests
-// =============================================================================
-
-const testing = std.testing;
-
-test "newUuidV7: produces 36-char hyphenated string with version 7" {
-    const io = testing.io;
-    const id = try newUuidV7(testing.allocator, io);
-    defer testing.allocator.free(id);
-    try testing.expectEqual(@as(usize, 36), id.len);
-    // Position 14 is the version nibble — should be '7'.
-    try testing.expectEqual(@as(u8, '7'), id[14]);
-    // Hyphens at canonical positions.
-    try testing.expectEqual(@as(u8, '-'), id[8]);
-    try testing.expectEqual(@as(u8, '-'), id[13]);
-    try testing.expectEqual(@as(u8, '-'), id[18]);
-    try testing.expectEqual(@as(u8, '-'), id[23]);
-}
-
-test "isoTimestamp: well-formed ISO 8601 with millisecond precision" {
-    const ts = try isoTimestamp(testing.allocator, testing.io);
-    defer testing.allocator.free(ts);
-    try testing.expectEqual(@as(usize, 24), ts.len);
-    try testing.expectEqual(@as(u8, '-'), ts[4]);
-    try testing.expectEqual(@as(u8, 'T'), ts[10]);
-    try testing.expectEqual(@as(u8, '.'), ts[19]);
-    try testing.expectEqual(@as(u8, 'Z'), ts[23]);
-}
-
-// ---- In-memory + filesystem tests (use a tmp dir) ----
-
-const TmpSessionDir = struct {
-    parent: std.testing.TmpDir,
-    abs_path: []u8,
-
-    fn init(allocator: Allocator) !TmpSessionDir {
-        var parent = std.testing.tmpDir(.{});
-        errdefer parent.cleanup();
-        var path_buf: [std.fs.max_path_bytes]u8 = undefined;
-        const n = try parent.dir.realPath(testing.io, &path_buf);
-        const abs = try allocator.dupe(u8, path_buf[0..n]);
-        return .{ .parent = parent, .abs_path = abs };
-    }
-
-    fn deinit(self: *TmpSessionDir, allocator: Allocator) void {
-        allocator.free(self.abs_path);
-        self.parent.cleanup();
-    }
-};
-
-test "SessionManager.init: does not create file yet" {
-    const io = testing.io;
-
-    var td = try TmpSessionDir.init(testing.allocator);
-    defer td.deinit(testing.allocator);
-
-    // Use a non-existent subdirectory inside the tmp dir to also exercise
-    // lazy directory creation.
-    const sessions = try std.fs.path.join(testing.allocator, &.{ td.abs_path, "sessions" });
-    defer testing.allocator.free(sessions);
-
-    var mgr = try SessionManager.init(
-        testing.allocator,
-        io,
-        sessions,
-        "/some/cwd",
-    );
-    defer mgr.deinit();
-
-    try testing.expect(!mgr.isFlushed());
-
-    // The directory should not exist yet.
-    const stat_err = Io.Dir.cwd().openDir(io, sessions, .{});
-    try testing.expectError(error.FileNotFound, stat_err);
-}
-
-test "SessionManager: full flow — buffer, flush on assistant, append, resume" {
-    const io = testing.io;
-
-    var td = try TmpSessionDir.init(testing.allocator);
-    defer td.deinit(testing.allocator);
-
-    const sessions = try std.fs.path.join(testing.allocator, &.{ td.abs_path, "sessions" });
-    defer testing.allocator.free(sessions);
-
-    const session_file: []u8 = blk: {
-        var mgr = try SessionManager.init(
-            testing.allocator,
-            io,
-            sessions,
-            "/proj/foo",
-        );
-        defer mgr.deinit();
-
-        // System message — non-assistant, should NOT trigger flush.
-        const sys_blocks = try testing.allocator.alloc(DiskContentBlock, 1);
-        sys_blocks[0] = .{ .text = .{ .text = try testing.allocator.dupe(u8, "You are helpful.") } };
-        _ = try mgr.appendMessage(
-            .{ .role = .system, .content = sys_blocks },
-            null,
-            null,
-        );
-        try testing.expect(!mgr.isFlushed());
-
-        // User message — also doesn't flush.
-        const usr_blocks = try testing.allocator.alloc(DiskContentBlock, 1);
-        usr_blocks[0] = .{ .text = .{ .text = try testing.allocator.dupe(u8, "hi there") } };
-        _ = try mgr.appendMessage(
-            .{ .role = .user, .content = usr_blocks },
-            "openai",
-            "gpt-4o",
-        );
-        try testing.expect(!mgr.isFlushed());
-
-        // Assistant message — triggers flush.
-        const a_blocks = try testing.allocator.alloc(DiskContentBlock, 1);
-        a_blocks[0] = .{ .text = .{ .text = try testing.allocator.dupe(u8, "hello") } };
-        _ = try mgr.appendMessage(
-            .{
-                .role = .assistant,
-                .content = a_blocks,
-                .provider = try testing.allocator.dupe(u8, "openai"),
-                .model = try testing.allocator.dupe(u8, "gpt-4o"),
-                .stop_reason = try testing.allocator.dupe(u8, "stop"),
-            },
-            null,
-            null,
-        );
-        try testing.expect(mgr.isFlushed());
-
-        // Append another user/assistant round.
-        const u_two = try testing.allocator.alloc(DiskContentBlock, 1);
-        u_two[0] = .{ .text = .{ .text = try testing.allocator.dupe(u8, "what's 2+2?") } };
-        _ = try mgr.appendMessage(.{ .role = .user, .content = u_two }, "openai", "gpt-4o");
-
-        const a2 = try testing.allocator.alloc(DiskContentBlock, 1);
-        a2[0] = .{ .text = .{ .text = try testing.allocator.dupe(u8, "4") } };
-        _ = try mgr.appendMessage(
-            .{ .role = .assistant, .content = a2, .stop_reason = try testing.allocator.dupe(u8, "stop") },
-            null,
-            null,
-        );
-
-        try testing.expectEqual(@as(usize, 5), mgr.getEntries().len);
-
-        break :blk try testing.allocator.dupe(u8, mgr.getSessionFile());
-    };
-    defer testing.allocator.free(session_file);
-
-    // Verify the file exists and is well-formed.
-    {
-        const bytes = try readWholeFile(testing.allocator, io, session_file);
-        defer testing.allocator.free(bytes);
-        // 1 header + 5 entries + trailing \n on each = 6 newlines.
-        var nl_count: usize = 0;
-        for (bytes) |b| if (b == '\n') {
-            nl_count += 1;
-        };
-        try testing.expectEqual(@as(usize, 6), nl_count);
-    }
-
-    // Resume.
-    var resumed = try SessionManager.open(testing.allocator, io, session_file);
-    defer resumed.deinit();
-    try testing.expect(resumed.isFlushed());
-    try testing.expectEqual(@as(usize, 5), resumed.getEntries().len);
-    try testing.expectEqualStrings("/proj/foo", resumed.getCwd());
-
-    // Continue the conversation.
-    const u_three = try testing.allocator.alloc(DiskContentBlock, 1);
-    u_three[0] = .{ .text = .{ .text = try testing.allocator.dupe(u8, "thanks") } };
-    _ = try resumed.appendMessage(.{ .role = .user, .content = u_three }, "openai", "gpt-4o");
-    try testing.expectEqual(@as(usize, 6), resumed.getEntries().len);
-}
-
-test "SessionManager: assistant message tags the message metadata and the entry leaf id is the assistant entry" {
-    const io = testing.io;
-
-    var td = try TmpSessionDir.init(testing.allocator);
-    defer td.deinit(testing.allocator);
-    const sessions = try std.fs.path.join(testing.allocator, &.{ td.abs_path, "sessions" });
-    defer testing.allocator.free(sessions);
-
-    var mgr = try SessionManager.init(testing.allocator, io, sessions, "/c");
-    defer mgr.deinit();
-
-    const u_blocks = try testing.allocator.alloc(DiskContentBlock, 1);
-    u_blocks[0] = .{ .text = .{ .text = try testing.allocator.dupe(u8, "ping") } };
-    const user_id = try mgr.appendMessage(.{ .role = .user, .content = u_blocks }, "openai", "gpt-4o");
-
-    const a_blocks = try testing.allocator.alloc(DiskContentBlock, 1);
-    a_blocks[0] = .{ .text = .{ .text = try testing.allocator.dupe(u8, "pong") } };
-    const asst_id = try mgr.appendMessage(.{ .role = .assistant, .content = a_blocks }, null, null);
-
-    // Leaf is the assistant entry.
-    try testing.expectEqualStrings(asst_id, mgr.getLeafId().?);
-    // Parent of assistant is the user entry.
-    const assistant_entry = mgr.getEntry(asst_id).?;
-    try testing.expectEqualStrings(user_id, assistant_entry.base().parent_id.?);
-    // User entry's parent is null (no system).
-    const user_entry = mgr.getEntry(user_id).?;
-    try testing.expect(user_entry.base().parent_id == null);
-}
-
-test "SessionManager: activeModel is null before any user message, then tracks the latest user stamp" {
-    const io = testing.io;
-
-    var td = try TmpSessionDir.init(testing.allocator);
-    defer td.deinit(testing.allocator);
-    const sessions = try std.fs.path.join(testing.allocator, &.{ td.abs_path, "sessions" });
-    defer testing.allocator.free(sessions);
-
-    var mgr = try SessionManager.init(testing.allocator, io, sessions, "/c");
-    defer mgr.deinit();
-
-    // No user messages yet — there is no "active" model on disk yet.
-    try testing.expect(mgr.activeModel() == null);
-
-    // Stamp a user message with anthropic.
-    const u_blocks = try testing.allocator.alloc(DiskContentBlock, 1);
-    u_blocks[0] = .{ .text = .{ .text = try testing.allocator.dupe(u8, "hi") } };
-    _ = try mgr.appendMessage(.{ .role = .user, .content = u_blocks }, "anthropic", "claude-sonnet-4-20250514");
-
-    {
-        const am = mgr.activeModel().?;
-        try testing.expectEqualStrings("anthropic", am.provider);
-        try testing.expectEqualStrings("claude-sonnet-4-20250514", am.model);
-    }
-}
-
-test "SessionManager: rebuildConversation reconstructs system/user/assistant turn" {
-    const io = testing.io;
-
-    var td = try TmpSessionDir.init(testing.allocator);
-    defer td.deinit(testing.allocator);
-    const sessions = try std.fs.path.join(testing.allocator, &.{ td.abs_path, "sessions" });
-    defer testing.allocator.free(sessions);
-
-    var mgr = try SessionManager.init(testing.allocator, io, sessions, "/c");
-    defer mgr.deinit();
-
-    const sys = try testing.allocator.alloc(DiskContentBlock, 1);
-    sys[0] = .{ .text = .{ .text = try testing.allocator.dupe(u8, "you are helpful") } };
-    _ = try mgr.appendMessage(.{ .role = .system, .content = sys }, null, null);
-
-    const u = try testing.allocator.alloc(DiskContentBlock, 1);
-    u[0] = .{ .text = .{ .text = try testing.allocator.dupe(u8, "hello") } };
-    _ = try mgr.appendMessage(.{ .role = .user, .content = u }, "openai", "gpt-4o");
-
-    const a = try testing.allocator.alloc(DiskContentBlock, 1);
-    a[0] = .{ .text = .{ .text = try testing.allocator.dupe(u8, "hi!") } };
-    _ = try mgr.appendMessage(.{ .role = .assistant, .content = a }, null, null);
-
-    var conv = try mgr.rebuildConversation();
-    defer conv.deinit();
-    try testing.expectEqual(@as(usize, 3), conv.messages.items.len);
-    try testing.expectEqual(conversation_mod.MessageRole.system, conv.messages.items[0].role);
-    try testing.expectEqualStrings("you are helpful", conv.messages.items[0].content.items[0].System.text.items);
-    try testing.expectEqual(conversation_mod.MessageRole.user, conv.messages.items[1].role);
-    try testing.expectEqualStrings("hello", conv.messages.items[1].content.items[0].Text.items);
-    try testing.expectEqual(conversation_mod.MessageRole.assistant, conv.messages.items[2].role);
-    try testing.expectEqualStrings("hi!", conv.messages.items[2].content.items[0].Text.items);
-}
-
-test "SessionManager: crash recovery truncates corrupted trailing line" {
-    const io = testing.io;
-
-    var td = try TmpSessionDir.init(testing.allocator);
-    defer td.deinit(testing.allocator);
-    const sessions = try std.fs.path.join(testing.allocator, &.{ td.abs_path, "sessions" });
-    defer testing.allocator.free(sessions);
-
-    // Build a valid session first.
-    const session_file: []u8 = blk: {
-        var mgr = try SessionManager.init(testing.allocator, io, sessions, "/c");
-        defer mgr.deinit();
-        const u = try testing.allocator.alloc(DiskContentBlock, 1);
-        u[0] = .{ .text = .{ .text = try testing.allocator.dupe(u8, "ping") } };
-        _ = try mgr.appendMessage(.{ .role = .user, .content = u }, "openai", "gpt-4o");
-        const a = try testing.allocator.alloc(DiskContentBlock, 1);
-        a[0] = .{ .text = .{ .text = try testing.allocator.dupe(u8, "pong") } };
-        _ = try mgr.appendMessage(.{ .role = .assistant, .content = a }, null, null);
-        break :blk try testing.allocator.dupe(u8, mgr.getSessionFile());
-    };
-    defer testing.allocator.free(session_file);
-
-    // Corrupt the file: append a partial JSON line at the end.
-    const garbage = "{\"type\":\"message\",\"id\":\"deadbeef\",\"parent";
-    {
-        const file = try Io.Dir.cwd().openFile(io, session_file, .{ .mode = .write_only });
-        defer file.close(io);
-        const len = try file.length(io);
-        try file.writePositionalAll(io, garbage, len);
-    }
-    // Confirm the file got bigger.
-    {
-        const f = try Io.Dir.cwd().openFile(io, session_file, .{ .mode = .read_only });
-        defer f.close(io);
-        const corrupted_len = try f.length(io);
-        try testing.expect(corrupted_len > garbage.len);
-    }
-
-    // Now resume — the partial line should be truncated.
-    var resumed = try SessionManager.open(testing.allocator, io, session_file);
-    defer resumed.deinit();
-    try testing.expectEqual(@as(usize, 2), resumed.getEntries().len);
-
-    // And the file on disk should match.
-    {
-        const bytes = try readWholeFile(testing.allocator, io, session_file);
-        defer testing.allocator.free(bytes);
-        try testing.expect(!std.mem.endsWith(u8, bytes, "parent"));
-        // Should end with a newline after the assistant entry.
-        try testing.expectEqual(@as(u8, '\n'), bytes[bytes.len - 1]);
-    }
-}
-
-test "listSessions: returns most recent first, with counts" {
-    const io = testing.io;
-
-    var td = try TmpSessionDir.init(testing.allocator);
-    defer td.deinit(testing.allocator);
-    const sessions = try std.fs.path.join(testing.allocator, &.{ td.abs_path, "sessions" });
-    defer testing.allocator.free(sessions);
-
-    // Create two sessions.
-    for (0..2) |i| {
-        var mgr = try SessionManager.init(testing.allocator, io, sessions, "/c");
-        defer mgr.deinit();
-        const u = try testing.allocator.alloc(DiskContentBlock, 1);
-        u[0] = .{ .text = .{ .text = try testing.allocator.dupe(u8, "u") } };
-        _ = try mgr.appendMessage(.{ .role = .user, .content = u }, "openai", "gpt-4o");
-        const a = try testing.allocator.alloc(DiskContentBlock, 1);
-        a[0] = .{ .text = .{ .text = try testing.allocator.dupe(u8, "a") } };
-        _ = try mgr.appendMessage(.{ .role = .assistant, .content = a }, null, null);
-        // Small sleep so UUIDv7 timestamps differ.
-        io.sleep(.fromMilliseconds(2), .real) catch {};
-        _ = i;
-    }
-
-    const infos = try listSessions(testing.allocator, io, sessions, null);
-    defer freeSessionInfos(testing.allocator, infos);
-    try testing.expectEqual(@as(usize, 2), infos.len);
-    try testing.expectEqual(@as(usize, 2), infos[0].message_count);
-    try testing.expect(std.mem.order(u8, infos[0].modified, infos[1].modified) != .lt);
-}
-
-test "findMostRecentSession: picks lexicographically greatest" {
-    const io = testing.io;
-
-    var td = try TmpSessionDir.init(testing.allocator);
-    defer td.deinit(testing.allocator);
-    const sessions = try std.fs.path.join(testing.allocator, &.{ td.abs_path, "sessions" });
-    defer testing.allocator.free(sessions);
-
-    // Pre-resolution before any sessions exist → null.
-    try testing.expect((try findMostRecentSession(testing.allocator, io, sessions)) == null);
-
-    // Create two.
-    var second_file: ?[]u8 = null;
-    defer if (second_file) |s| testing.allocator.free(s);
-
-    for (0..2) |i| {
-        var mgr = try SessionManager.init(testing.allocator, io, sessions, "/c");
-        defer mgr.deinit();
-        const u = try testing.allocator.alloc(DiskContentBlock, 1);
-        u[0] = .{ .text = .{ .text = try testing.allocator.dupe(u8, "u") } };
-        _ = try mgr.appendMessage(.{ .role = .user, .content = u }, "openai", "gpt-4o");
-        const a = try testing.allocator.alloc(DiskContentBlock, 1);
-        a[0] = .{ .text = .{ .text = try testing.allocator.dupe(u8, "a") } };
-        _ = try mgr.appendMessage(.{ .role = .assistant, .content = a }, null, null);
-        if (i == 1) second_file = try testing.allocator.dupe(u8, mgr.getSessionFile());
-        io.sleep(.fromMilliseconds(2), .real) catch {};
-    }
-
-    const found = (try findMostRecentSession(testing.allocator, io, sessions)).?;
-    defer testing.allocator.free(found);
-    try testing.expectEqualStrings(second_file.?, found);
-}
-
-test "SessionManager: tool-use round-trip — assistant w/ ToolUse, user w/ ToolResult, assistant" {
-    const io = testing.io;
-    var td = try TmpSessionDir.init(testing.allocator);
-    defer td.deinit(testing.allocator);
-    const sessions = try std.fs.path.join(testing.allocator, &.{ td.abs_path, "sessions" });
-    defer testing.allocator.free(sessions);
-
-    const session_file: []u8 = blk: {
-        var mgr = try SessionManager.init(testing.allocator, io, sessions, "/c");
-        defer mgr.deinit();
-
-        const u = try testing.allocator.alloc(DiskContentBlock, 1);
-        u[0] = .{ .text = .{ .text = try testing.allocator.dupe(u8, "list files") } };
-        _ = try mgr.appendMessage(.{ .role = .user, .content = u }, "openai", "gpt-4o");
-
-        // Assistant emits a ToolUse.
-        const am1 = try testing.allocator.alloc(DiskContentBlock, 2);
-        am1[0] = .{ .text = .{ .text = try testing.allocator.dupe(u8, "checking...") } };
-        am1[1] = .{ .tool_use = .{
-            .id = try testing.allocator.dupe(u8, "tool_abc"),
-            .name = try testing.allocator.dupe(u8, "bash"),
-            .input = try testing.allocator.dupe(u8, "{\"command\":\"ls\"}"),
-        } };
-        _ = try mgr.appendMessage(.{ .role = .assistant, .content = am1 }, null, null);
-
-        // Tool-result user message.
-        const tr = try testing.allocator.alloc(DiskContentBlock, 1);
-        const trp = try testing.allocator.alloc(session_mod.DiskResultPart, 1);
-        trp[0] = .{ .text = try testing.allocator.dupe(u8, "a.txt\nb.txt") };
-        tr[0] = .{ .tool_result = .{
-            .tool_use_id = try testing.allocator.dupe(u8, "tool_abc"),
-            .parts = trp,
-        } };
-        _ = try mgr.appendMessage(.{ .role = .user, .content = tr }, "openai", "gpt-4o");
-
-        // Final assistant reply.
-        const a2 = try testing.allocator.alloc(DiskContentBlock, 1);
-        a2[0] = .{ .text = .{ .text = try testing.allocator.dupe(u8, "two files: a.txt and b.txt") } };
-        _ = try mgr.appendMessage(.{ .role = .assistant, .content = a2 }, null, null);
-
-        break :blk try testing.allocator.dupe(u8, mgr.getSessionFile());
-    };
-    defer testing.allocator.free(session_file);
-
-    // Reopen and verify content blocks survive.
-    var resumed = try SessionManager.open(testing.allocator, io, session_file);
-    defer resumed.deinit();
-    const entries = resumed.getEntries();
-    try testing.expectEqual(@as(usize, 4), entries.len);
-
-    // [1] = assistant with ToolUse
-    try testing.expectEqual(DiskMessageRole.assistant, entries[1].message.message.role);
-    try testing.expectEqual(@as(usize, 2), entries[1].message.message.content.len);
-    try testing.expect(entries[1].message.message.content[1] == .tool_use);
-    try testing.expectEqualStrings("bash", entries[1].message.message.content[1].tool_use.name);
-    try testing.expectEqualStrings("{\"command\":\"ls\"}", entries[1].message.message.content[1].tool_use.input);
-
-    // [2] = user with ToolResult, stamped with provider/model.
-    try testing.expectEqual(DiskMessageRole.user, entries[2].message.message.role);
-    try testing.expectEqualStrings("openai", entries[2].message.provider.?);
-    try testing.expect(entries[2].message.message.content[0] == .tool_result);
-    try testing.expectEqualStrings("tool_abc", entries[2].message.message.content[0].tool_result.tool_use_id);
-    try testing.expectEqualStrings("a.txt\nb.txt", entries[2].message.message.content[0].tool_result.parts[0].text);
-
-    // Conversation rebuild yields the same shape.
-    var conv = try resumed.rebuildConversation();
-    defer conv.deinit();
-    try testing.expectEqual(@as(usize, 4), conv.messages.items.len);
-    try testing.expect(conv.messages.items[1].content.items[1] == .ToolUse);
-    try testing.expect(conv.messages.items[2].content.items[0] == .ToolResult);
-}
-
-test "SessionManager: linear chain — each entry's parent_id is the previous entry's id" {
-    const io = testing.io;
-    var td = try TmpSessionDir.init(testing.allocator);
-    defer td.deinit(testing.allocator);
-    const sessions = try std.fs.path.join(testing.allocator, &.{ td.abs_path, "sessions" });
-    defer testing.allocator.free(sessions);
-
-    var mgr = try SessionManager.init(testing.allocator, io, sessions, "/c");
-    defer mgr.deinit();
-
-    // Three rounds: sys, user, asst, user, asst.
-    const sys = try testing.allocator.alloc(DiskContentBlock, 1);
-    sys[0] = .{ .text = .{ .text = try testing.allocator.dupe(u8, "sys") } };
-    _ = try mgr.appendMessage(.{ .role = .system, .content = sys }, null, null);
-
-    const u_one = try testing.allocator.alloc(DiskContentBlock, 1);
-    u_one[0] = .{ .text = .{ .text = try testing.allocator.dupe(u8, "u1") } };
-    _ = try mgr.appendMessage(.{ .role = .user, .content = u_one }, "openai", "gpt-4o");
-
-    const a_one = try testing.allocator.alloc(DiskContentBlock, 1);
-    a_one[0] = .{ .text = .{ .text = try testing.allocator.dupe(u8, "a1") } };
-    _ = try mgr.appendMessage(.{ .role = .assistant, .content = a_one }, null, null);
-
-    const u_two = try testing.allocator.alloc(DiskContentBlock, 1);
-    u_two[0] = .{ .text = .{ .text = try testing.allocator.dupe(u8, "u2") } };
-    _ = try mgr.appendMessage(.{ .role = .user, .content = u_two }, "openai", "gpt-4o");
-
-    const a_two = try testing.allocator.alloc(DiskContentBlock, 1);
-    a_two[0] = .{ .text = .{ .text = try testing.allocator.dupe(u8, "a2") } };
-    _ = try mgr.appendMessage(.{ .role = .assistant, .content = a_two }, null, null);
-
-    const entries = mgr.getEntries();
-    try testing.expectEqual(@as(usize, 5), entries.len);
-    try testing.expect(entries[0].base().parent_id == null);
-    for (entries[1..], 1..) |e, i| {
-        try testing.expectEqualStrings(entries[i - 1].base().id, e.base().parent_id.?);
-    }
-}
-
-test "resolveSessionId: unique prefix → match, ambiguous → error" {
-    const io = testing.io;
-
-    var td = try TmpSessionDir.init(testing.allocator);
-    defer td.deinit(testing.allocator);
-    const sessions = try std.fs.path.join(testing.allocator, &.{ td.abs_path, "sessions" });
-    defer testing.allocator.free(sessions);
-
-    // Create one session.
-    var mgr = try SessionManager.init(testing.allocator, io, sessions, "/c");
-    defer mgr.deinit();
-    const u = try testing.allocator.alloc(DiskContentBlock, 1);
-    u[0] = .{ .text = .{ .text = try testing.allocator.dupe(u8, "u") } };
-    _ = try mgr.appendMessage(.{ .role = .user, .content = u }, "openai", "gpt-4o");
-    const a = try testing.allocator.alloc(DiskContentBlock, 1);
-    a[0] = .{ .text = .{ .text = try testing.allocator.dupe(u8, "a") } };
-    _ = try mgr.appendMessage(.{ .role = .assistant, .content = a }, null, null);
-
-    const id = mgr.getSessionId();
-    const prefix = id[0..8];
-
-    const resolved = try resolveSessionId(testing.allocator, io, sessions, prefix);
-    defer testing.allocator.free(resolved);
-    try testing.expectEqualStrings(mgr.getSessionFile(), resolved);
-
-    try testing.expectError(error.SessionNotFound, resolveSessionId(testing.allocator, io, sessions, "ffffffff"));
-}
-
-test "compaction summary round-trips through persist + resume + rebuild" {
-    const io = testing.io;
-
-    var td = try TmpSessionDir.init(testing.allocator);
-    defer td.deinit(testing.allocator);
-    const sessions = try std.fs.path.join(testing.allocator, &.{ td.abs_path, "sessions" });
-    defer testing.allocator.free(sessions);
-
-    const session_file: []u8 = blk: {
-        var mgr = try SessionManager.init(testing.allocator, io, sessions, "/c");
-        defer mgr.deinit();
-
-        // System + an old turn that will be superseded.
-        const sys = try testing.allocator.alloc(DiskContentBlock, 1);
-        sys[0] = .{ .text = .{ .text = try testing.allocator.dupe(u8, "you are helpful") } };
-        _ = try mgr.appendMessage(.{ .role = .system, .content = sys }, null, null);
-
-        const uo = try testing.allocator.alloc(DiskContentBlock, 1);
-        uo[0] = .{ .text = .{ .text = try testing.allocator.dupe(u8, "old q") } };
-        _ = try mgr.appendMessage(.{ .role = .user, .content = uo }, "openai", "gpt-4o");
-        const ao = try testing.allocator.alloc(DiskContentBlock, 1);
-        ao[0] = .{ .text = .{ .text = try testing.allocator.dupe(u8, "old a") } };
-        _ = try mgr.appendMessage(.{ .role = .assistant, .content = ao }, null, null);
-
-        // Compaction: summary message + duplicated kept suffix.
-        const cs = try testing.allocator.alloc(DiskContentBlock, 1);
-        cs[0] = .{ .compaction_summary = .{ .text = try testing.allocator.dupe(u8, "SUMMARY") } };
-        _ = try mgr.appendMessage(.{ .role = .user, .content = cs }, "openai", "gpt-4o");
-
-        const ur = try testing.allocator.alloc(DiskContentBlock, 1);
-        ur[0] = .{ .text = .{ .text = try testing.allocator.dupe(u8, "recent q") } };
-        _ = try mgr.appendMessage(.{ .role = .user, .content = ur }, "openai", "gpt-4o");
-
-        break :blk try testing.allocator.dupe(u8, mgr.getSessionFile());
-    };
-    defer testing.allocator.free(session_file);
-
-    var resumed = try SessionManager.open(testing.allocator, io, session_file);
-    defer resumed.deinit();
-    var conv = try resumed.rebuildConversation();
-    defer conv.deinit();
-
-    // The compaction summary block survived as a CompactionSummary.
-    const anchor = conversation_mod.latestCompactionIndex(conv.messages.items).?;
-    try testing.expectEqualStrings(
-        "SUMMARY",
-        conv.messages.items[anchor].content.items[0].CompactionSummary.text.items,
-    );
-
-    // The active window is [summary, recent q].
-    const window = conversation_mod.activeMessageWindow(conv.messages.items);
-    try testing.expectEqual(@as(usize, 2), window.len);
-    try testing.expectEqualStrings("recent q", window[1].content.items[0].Text.items);
-
-    // System prompt survives (derived independently).
-    var sys_blocks = try conversation_mod.effectiveSystemBlocks(testing.allocator, conv.messages.items);
-    defer sys_blocks.deinit(testing.allocator);
-    try testing.expectEqual(@as(usize, 1), sys_blocks.items.len);
-    try testing.expectEqualStrings("you are helpful", sys_blocks.items[0]);
-}
-
-test "loadConversation: trailing user prompt is split out as dangling, excluded from conversation" {
-    const io = testing.io;
-
-    var td = try TmpSessionDir.init(testing.allocator);
-    defer td.deinit(testing.allocator);
-    const sessions = try std.fs.path.join(testing.allocator, &.{ td.abs_path, "sessions" });
-    defer testing.allocator.free(sessions);
-
-    var mgr = try SessionManager.init(testing.allocator, io, sessions, "/c");
-    defer mgr.deinit();
-
-    // A completed user/assistant round, then a dangling user prompt with no
-    // following assistant (simulating a crash right after submission).
-    const um1 = try testing.allocator.alloc(DiskContentBlock, 1);
-    um1[0] = .{ .text = .{ .text = try testing.allocator.dupe(u8, "hi") } };
-    _ = try mgr.appendMessage(.{ .role = .user, .content = um1 }, "openai", "gpt-4o");
-    const am1 = try testing.allocator.alloc(DiskContentBlock, 1);
-    am1[0] = .{ .text = .{ .text = try testing.allocator.dupe(u8, "hello") } };
-    _ = try mgr.appendMessage(.{ .role = .assistant, .content = am1 }, null, null);
-    const um2 = try testing.allocator.alloc(DiskContentBlock, 1);
-    um2[0] = .{ .text = .{ .text = try testing.allocator.dupe(u8, "what's 2+2?") } };
-    _ = try mgr.appendMessage(.{ .role = .user, .content = um2 }, "openai", "gpt-4o");
-
-    var loaded = try mgr.loadConversation(testing.allocator);
-    defer loaded.deinit(testing.allocator);
-
-    // Dangling prompt recovered.
-    try testing.expect(loaded.dangling_user != null);
-    try testing.expectEqualStrings("what's 2+2?", loaded.dangling_user.?);
-    // Conversation excludes the dangling user turn: [user hi, assistant hello].
-    try testing.expectEqual(@as(usize, 2), loaded.conversation.messages.items.len);
-    try testing.expectEqual(conversation_mod.MessageRole.user, loaded.conversation.messages.items[0].role);
-    try testing.expectEqual(conversation_mod.MessageRole.assistant, loaded.conversation.messages.items[1].role);
-}
-
-test "loadConversation: no dangling prompt when log ends with assistant" {
-    const io = testing.io;
-
-    var td = try TmpSessionDir.init(testing.allocator);
-    defer td.deinit(testing.allocator);
-    const sessions = try std.fs.path.join(testing.allocator, &.{ td.abs_path, "sessions" });
-    defer testing.allocator.free(sessions);
-
-    var mgr = try SessionManager.init(testing.allocator, io, sessions, "/c");
-    defer mgr.deinit();
-
-    const um1 = try testing.allocator.alloc(DiskContentBlock, 1);
-    um1[0] = .{ .text = .{ .text = try testing.allocator.dupe(u8, "hi") } };
-    _ = try mgr.appendMessage(.{ .role = .user, .content = um1 }, "openai", "gpt-4o");
-    const am1 = try testing.allocator.alloc(DiskContentBlock, 1);
-    am1[0] = .{ .text = .{ .text = try testing.allocator.dupe(u8, "hello") } };
-    _ = try mgr.appendMessage(.{ .role = .assistant, .content = am1 }, null, null);
-
-    var loaded = try mgr.loadConversation(testing.allocator);
-    defer loaded.deinit(testing.allocator);
-    try testing.expect(loaded.dangling_user == null);
-    try testing.expectEqual(@as(usize, 2), loaded.conversation.messages.items.len);
-}
-
-test "store(): SessionStore wrapper delegates to the concrete manager" {
-    const io = testing.io;
-
-    var td = try TmpSessionDir.init(testing.allocator);
-    defer td.deinit(testing.allocator);
-    const sessions = try std.fs.path.join(testing.allocator, &.{ td.abs_path, "sessions" });
-    defer testing.allocator.free(sessions);
-
-    var mgr = try SessionManager.init(testing.allocator, io, sessions, "/c");
-    defer mgr.deinit();
-
-    const s = mgr.store();
-
-    // Append a user+assistant batch through the neutral interface.
-    var messages = try testing.allocator.alloc(DiskMessage, 2);
-    defer testing.allocator.free(messages);
-    const uc = try testing.allocator.alloc(DiskContentBlock, 1);
-    uc[0] = .{ .text = .{ .text = try testing.allocator.dupe(u8, "ping") } };
-    messages[0] = .{ .role = .user, .content = uc };
-    const ac = try testing.allocator.alloc(DiskContentBlock, 1);
-    ac[0] = .{ .text = .{ .text = try testing.allocator.dupe(u8, "pong") } };
-    messages[1] = .{ .role = .assistant, .content = ac };
-
-    try s.appendMessages(messages, &.{ "openai", null }, &.{ "gpt-4o", null });
-    try testing.expectEqual(@as(usize, 2), mgr.getEntries().len);
-
-    const am = s.activeModel().?;
-    try testing.expectEqualStrings("openai", am.provider);
-    try testing.expectEqualStrings("gpt-4o", am.model);
-    try testing.expectEqualStrings(mgr.getSessionId(), s.sessionId());
-}