initial commit, moved libpanto over from the pantograph repo

1 files changed, 1606 insertions, 0 deletions

diff --git a/src/session.zig b/src/session.zig
new file mode 100644
index 0000000..35fd09b
--- /dev/null
+++ b/src/session.zig
@@ -0,0 +1,1606 @@
+//! On-disk session entry types and JSON serialization.
+//!
+//! These types are the wire format of pantograph's session log. They are
+//! intentionally separate from the in-memory `Conversation`/`Message`/
+//! `ContentBlock` model:
+//!
+//!   - The in-memory model holds only what providers need to serialize a
+//!     request (`role`, `content`).
+//!   - The on-disk model holds the full event-log story: provider/model
+//!     used per request, assistant stop reason and usage, timestamps, and
+//!     enough tree structure (`id`/`parent_id`) to allow future branching.
+//!
+//! Bridge functions at the bottom convert between the two. The bridge is
+//! lossy by design: assistant metadata (provider/model/stop_reason/usage)
+//! is recorded in entries but does NOT round-trip into the in-memory
+//! conversation, because providers don't need it for request serialization.
+//!
+//! Format version: 1 (see `CURRENT_VERSION`). No prior versions exist;
+//! when v2 lands, a migration step on load can transform v1 entries.
+
+const std = @import("std");
+const Allocator = std.mem.Allocator;
+const Writer = std.Io.Writer;
+
+const conversation = @import("conversation.zig");
+const config = @import("config.zig");
+
+pub const APIStyle = config.APIStyle;
+pub const ReasoningEffort = config.ReasoningEffort;
+pub const Thinking = config.Thinking;
+pub const Effort = config.Effort;
+
+/// Wire-format provider identity stamped on a message entry. This is the
+/// ground truth of which endpoint a turn was sent to — never a CLI config
+/// alias, and never any `api_key` material. Recorded on user/assistant
+/// entries; null on system entries.
+pub const WireStamp = struct {
+    api_style: APIStyle,
+    base_url: []const u8, // owned
+    model: []const u8, // owned
+    /// OpenAI only. Defaults to `.default` (field omitted on the wire).
+    reasoning: ReasoningEffort = .default,
+    /// Anthropic only. Defaults to `.enabled`.
+    thinking: Thinking = .enabled,
+    /// Anthropic only; only meaningful when `thinking == .adaptive`.
+    effort: Effort = .medium,
+    /// Anthropic only; only meaningful when `thinking == .enabled`. `null`
+    /// means "use the config default" (falls back to `max_tokens - 1`).
+    thinking_budget_tokens: ?u32 = 32_000,
+    /// Anthropic only; only meaningful when `thinking == .enabled`.
+    thinking_interleaved: bool = false,
+
+    pub fn deinit(self: WireStamp, alloc: Allocator) void {
+        alloc.free(self.base_url);
+        alloc.free(self.model);
+    }
+
+    pub fn dupe(self: WireStamp, alloc: Allocator) !WireStamp {
+        const burl = try alloc.dupe(u8, self.base_url);
+        errdefer alloc.free(burl);
+        const mdl = try alloc.dupe(u8, self.model);
+        return .{
+            .api_style = self.api_style,
+            .base_url = burl,
+            .model = mdl,
+            .reasoning = self.reasoning,
+            .thinking = self.thinking,
+            .effort = self.effort,
+            .thinking_budget_tokens = self.thinking_budget_tokens,
+            .thinking_interleaved = self.thinking_interleaved,
+        };
+    }
+};
+
+/// Bumped whenever the on-disk format changes in a way that older readers
+/// cannot tolerate. When that happens, add a load-time migration that
+/// upgrades older files and rewrites them once.
+pub const CURRENT_VERSION: u32 = 1;
+
+// =============================================================================
+// Header
+// =============================================================================
+
+/// First (and only) line of a session file. Metadata only — not part of
+/// the entry tree (no id/parent_id).
+pub const SessionHeader = struct {
+    version: u32,
+    id: []const u8, // UUIDv7 string, owned
+    timestamp: []const u8, // ISO 8601, owned
+    /// Opaque session-wide metadata bag. Round-trips verbatim; `libpanto`
+    /// never interprets it. The panto CLI records `{ "cwd": ... }` here.
+    metadata: ?[]const u8 = null, // owned
+
+    pub fn deinit(self: SessionHeader, alloc: Allocator) void {
+        alloc.free(self.id);
+        alloc.free(self.timestamp);
+        if (self.metadata) |m| alloc.free(m);
+    }
+};
+
+// =============================================================================
+// Entries
+// =============================================================================
+
+/// Fields shared by every non-header entry.
+pub const EntryBase = struct {
+    id: []const u8, // 8-char hex, owned
+    parent_id: ?[]const u8, // owned, null for first entry
+    timestamp: []const u8, // ISO 8601, owned
+
+    pub fn deinit(self: EntryBase, alloc: Allocator) void {
+        alloc.free(self.id);
+        if (self.parent_id) |p| alloc.free(p);
+        alloc.free(self.timestamp);
+    }
+};
+
+pub const SessionEntry = union(enum) {
+    message: MessageEntry,
+
+    pub fn base(self: SessionEntry) EntryBase {
+        return switch (self) {
+            .message => |m| m.base,
+        };
+    }
+
+    pub fn deinit(self: SessionEntry, alloc: Allocator) void {
+        switch (self) {
+            .message => |m| m.deinit(alloc),
+        }
+    }
+};
+
+pub const MessageEntry = struct {
+    base: EntryBase,
+    /// Wire-format provider identity for this entry. Recorded on user and
+    /// assistant message entries (both are tied to a provider API call);
+    /// null on system entries.
+    stamp: ?WireStamp = null,
+    message: StoredMessage,
+
+    pub fn deinit(self: MessageEntry, alloc: Allocator) void {
+        self.base.deinit(alloc);
+        if (self.stamp) |s| s.deinit(alloc);
+        self.message.deinit(alloc);
+    }
+};
+
+pub const StoredMessageRole = enum { system, user, assistant };
+
+/// Mode for a system-role message. Mirrors `conversation.SystemMode`.
+/// `append` adds to the effective prompt; `replace` discards all prior
+/// system text. Only meaningful on system messages; absent on disk means
+/// `append` (back-compatible with pre-mode logs).
+pub const StoredSystemMode = enum { append, replace };
+
+pub const StoredMessage = struct {
+    role: StoredMessageRole,
+    content: []StoredContentBlock, // owned
+    /// System-message mode. Recorded only for system-role messages; an
+    /// absent `mode` on disk parses back as `.append`.
+    mode: StoredSystemMode = .append,
+    /// Assistant-only stop reason. Null for system/user messages.
+    stop_reason: ?[]const u8 = null, // owned
+    usage: ?Usage = null,
+    /// Opaque per-message metadata bag (see `conversation.Message.metadata`).
+    /// Round-trips verbatim; `libpanto` never interprets it.
+    metadata: ?[]const u8 = null, // owned
+
+    pub fn deinit(self: StoredMessage, alloc: Allocator) void {
+        for (self.content) |block| block.deinit(alloc);
+        alloc.free(self.content);
+        if (self.stop_reason) |s| alloc.free(s);
+        if (self.metadata) |m| alloc.free(m);
+    }
+};
+
+/// Token usage reported by a provider for a single assistant turn.
+///
+/// Defined in `conversation.zig` (so in-memory `Message`s can carry it
+/// without a module cycle) and re-exported here for the on-disk types and
+/// historical call sites that import it as `session.Usage`.
+pub const Usage = conversation.Usage;
+
+// =============================================================================
+// Content blocks
+// =============================================================================
+
+pub const StoredContentBlock = union(enum) {
+    text: StoredTextBlock,
+    thinking: StoredThinkingBlock,
+    tool_use: StoredToolUseBlock,
+    tool_result: StoredToolResultBlock,
+    compaction_summary: StoredCompactionSummaryBlock,
+
+    pub fn deinit(self: StoredContentBlock, alloc: Allocator) void {
+        switch (self) {
+            .text => |b| b.deinit(alloc),
+            .thinking => |b| b.deinit(alloc),
+            .tool_use => |b| b.deinit(alloc),
+            .tool_result => |b| b.deinit(alloc),
+            .compaction_summary => |b| b.deinit(alloc),
+        }
+    }
+};
+
+pub const StoredTextBlock = struct {
+    text: []const u8, // owned
+    pub fn deinit(self: StoredTextBlock, alloc: Allocator) void {
+        alloc.free(self.text);
+    }
+};
+
+pub const StoredThinkingBlock = struct {
+    thinking: []const u8, // owned
+    /// Anthropic's opaque integrity token. Other providers do not produce
+    /// one. Preserved here so resumed sessions can be sent back to
+    /// Anthropic with the original thinking block intact.
+    signature: ?[]const u8 = null, // owned
+    pub fn deinit(self: StoredThinkingBlock, alloc: Allocator) void {
+        alloc.free(self.thinking);
+        if (self.signature) |s| alloc.free(s);
+    }
+};
+
+pub const StoredToolUseBlock = struct {
+    id: []const u8, // owned
+    name: []const u8, // owned
+    input: []const u8, // raw JSON bytes, owned
+    pub fn deinit(self: StoredToolUseBlock, alloc: Allocator) void {
+        alloc.free(self.id);
+        alloc.free(self.name);
+        alloc.free(self.input);
+    }
+};
+
+/// One on-disk tool-result part: either text or an inline base64 media
+/// attachment (no sidecar files).
+pub const StoredResultPart = union(enum) {
+    text: []const u8, // owned
+    media: struct {
+        media_type: []const u8, // owned
+        data: []const u8, // owned (base64)
+    },
+    pub fn deinit(self: StoredResultPart, alloc: Allocator) void {
+        switch (self) {
+            .text => |t| alloc.free(t),
+            .media => |m| {
+                alloc.free(m.media_type);
+                alloc.free(m.data);
+            },
+        }
+    }
+};
+
+pub const StoredToolResultBlock = struct {
+    tool_use_id: []const u8, // owned
+    parts: []StoredResultPart, // owned
+    is_error: bool = false,
+    pub fn deinit(self: StoredToolResultBlock, alloc: Allocator) void {
+        alloc.free(self.tool_use_id);
+        for (self.parts) |p| p.deinit(alloc);
+        alloc.free(self.parts);
+    }
+};
+
+/// A compaction summary block: the synthetic seed text standing in for a
+/// compacted conversation prefix. Sits alone in a `user`-role message. See
+/// `conversation.CompactionSummaryBlock`.
+pub const StoredCompactionSummaryBlock = struct {
+    text: []const u8, // owned
+    pub fn deinit(self: StoredCompactionSummaryBlock, alloc: Allocator) void {
+        alloc.free(self.text);
+    }
+};
+
+// =============================================================================
+// File entry (header or entry)
+// =============================================================================
+
+pub const FileEntry = union(enum) {
+    header: SessionHeader,
+    entry: SessionEntry,
+
+    pub fn deinit(self: FileEntry, alloc: Allocator) void {
+        switch (self) {
+            .header => |h| h.deinit(alloc),
+            .entry => |e| e.deinit(alloc),
+        }
+    }
+};
+
+// =============================================================================
+// Serialization
+// =============================================================================
+
+/// Serialize the header as a single JSON line. Caller owns returned bytes.
+/// The returned slice does NOT include a trailing newline.
+pub fn serializeHeader(allocator: Allocator, header: SessionHeader) ![]u8 {
+    var aw: Writer.Allocating = .init(allocator);
+    errdefer aw.deinit();
+
+    var s: std.json.Stringify = .{ .writer = &aw.writer };
+    try s.beginObject();
+    try s.objectField("type");
+    try s.write("session");
+    try s.objectField("version");
+    try s.write(header.version);
+    try s.objectField("id");
+    try s.write(header.id);
+    try s.objectField("timestamp");
+    try s.write(header.timestamp);
+    if (header.metadata) |md| {
+        var parsed = try std.json.parseFromSlice(std.json.Value, allocator, md, .{});
+        defer parsed.deinit();
+        try s.objectField("metadata");
+        try s.write(parsed.value);
+    }
+    try s.endObject();
+
+    return try aw.toOwnedSlice();
+}
+
+/// Serialize an entry as a single JSON line. Caller owns returned bytes.
+pub fn serializeEntry(allocator: Allocator, entry: SessionEntry) ![]u8 {
+    var aw: Writer.Allocating = .init(allocator);
+    errdefer aw.deinit();
+    var s: std.json.Stringify = .{ .writer = &aw.writer };
+    try writeEntry(&s, entry);
+    return try aw.toOwnedSlice();
+}
+
+fn writeEntry(s: *std.json.Stringify, entry: SessionEntry) !void {
+    switch (entry) {
+        .message => |m| try writeMessageEntry(s, m),
+    }
+}
+
+fn writeMessageEntry(s: *std.json.Stringify, m: MessageEntry) !void {
+    try s.beginObject();
+    try s.objectField("type");
+    try s.write("message");
+    try s.objectField("id");
+    try s.write(m.base.id);
+    try s.objectField("parentId");
+    if (m.base.parent_id) |p| try s.write(p) else try s.write(null);
+    try s.objectField("timestamp");
+    try s.write(m.base.timestamp);
+    // Wire-format provider identity on user/assistant entries.
+    if (m.stamp) |st| try writeWireStamp(s, st);
+    try s.objectField("message");
+    try writeDiskMessage(s, m.message);
+    try s.endObject();
+}
+
+fn writeWireStamp(s: *std.json.Stringify, st: WireStamp) !void {
+    try s.objectField("apiStyle");
+    try s.write(@tagName(st.api_style));
+    try s.objectField("baseUrl");
+    try s.write(st.base_url);
+    try s.objectField("model");
+    try s.write(st.model);
+    // OpenAI: emit reasoning only when non-default (keeps logs compact).
+    if (st.reasoning != .default) {
+        try s.objectField("reasoning");
+        try s.write(@tagName(st.reasoning));
+    }
+    // Anthropic: emit thinking fields only when they differ from defaults.
+    if (st.thinking != .enabled) {
+        try s.objectField("thinking");
+        try s.write(@tagName(st.thinking));
+    }
+    if (st.effort != .medium) {
+        try s.objectField("effort");
+        try s.write(@tagName(st.effort));
+    }
+    if (st.thinking_budget_tokens) |b| {
+        if (b != 32_000) {
+            try s.objectField("thinkingBudgetTokens");
+            try s.write(b);
+        }
+    } else {
+        // null means "use max_tokens - 1"; record the absence explicitly
+        // so round-trips preserve the null intent.
+        try s.objectField("thinkingBudgetTokens");
+        try s.write(null);
+    }
+    if (st.thinking_interleaved) {
+        try s.objectField("thinkingInterleaved");
+        try s.write(true);
+    }
+}
+
+fn writeDiskMessage(s: *std.json.Stringify, msg: StoredMessage) !void {
+    try s.beginObject();
+    try s.objectField("role");
+    try s.write(@tagName(msg.role));
+    // `mode` is meaningful only for system messages. Emit it there so the
+    // append/replace semantics round-trip; omit it everywhere else.
+    if (msg.role == .system) {
+        try s.objectField("mode");
+        try s.write(@tagName(msg.mode));
+    }
+    try s.objectField("content");
+    try s.beginArray();
+    for (msg.content) |block| {
+        try writeDiskBlock(s, block);
+    }
+    try s.endArray();
+    if (msg.stop_reason) |sr| {
+        try s.objectField("stopReason");
+        try s.write(sr);
+    }
+    if (msg.metadata) |md| {
+        try s.objectField("metadata");
+        try s.write(md);
+    }
+    if (msg.usage) |u| {
+        try s.objectField("usage");
+        try s.beginObject();
+        try s.objectField("input");
+        try s.write(u.input);
+        try s.objectField("output");
+        try s.write(u.output);
+        // Omit zero-valued auxiliary fields to keep older / unused
+        // sessions compact. Readers default missing fields to 0, so
+        // round-trip behavior is preserved.
+        if (u.cache_read != 0) {
+            try s.objectField("cacheRead");
+            try s.write(u.cache_read);
+        }
+        if (u.cache_write != 0) {
+            try s.objectField("cacheWrite");
+            try s.write(u.cache_write);
+        }
+        if (u.reasoning != 0) {
+            try s.objectField("reasoning");
+            try s.write(u.reasoning);
+        }
+        try s.endObject();
+    }
+    try s.endObject();
+}
+
+fn writeDiskBlock(s: *std.json.Stringify, block: StoredContentBlock) !void {
+    switch (block) {
+        .text => |b| {
+            try s.beginObject();
+            try s.objectField("type");
+            try s.write("text");
+            try s.objectField("text");
+            try s.write(b.text);
+            try s.endObject();
+        },
+        .thinking => |b| {
+            try s.beginObject();
+            try s.objectField("type");
+            try s.write("thinking");
+            try s.objectField("thinking");
+            try s.write(b.thinking);
+            if (b.signature) |sig| {
+                try s.objectField("signature");
+                try s.write(sig);
+            }
+            try s.endObject();
+        },
+        .tool_use => |b| {
+            try s.beginObject();
+            try s.objectField("type");
+            try s.write("toolUse");
+            try s.objectField("id");
+            try s.write(b.id);
+            try s.objectField("name");
+            try s.write(b.name);
+            try s.objectField("input");
+            try s.write(b.input);
+            try s.endObject();
+        },
+        .tool_result => |b| {
+            try s.beginObject();
+            try s.objectField("type");
+            try s.write("toolResult");
+            try s.objectField("toolUseId");
+            try s.write(b.tool_use_id);
+            // Persist the error marker only when set, so existing
+            // (success) tool-result logs serialize byte-identically.
+            if (b.is_error) {
+                try s.objectField("isError");
+                try s.write(true);
+            }
+            // `parts` is an array of {type:"text",text} and
+            // {type:"image",mimeType,data} (data = inline base64).
+            try s.objectField("parts");
+            try s.beginArray();
+            for (b.parts) |part| {
+                switch (part) {
+                    .text => |t| {
+                        try s.beginObject();
+                        try s.objectField("type");
+                        try s.write("text");
+                        try s.objectField("text");
+                        try s.write(t);
+                        try s.endObject();
+                    },
+                    .media => |m| {
+                        try s.beginObject();
+                        try s.objectField("type");
+                        try s.write("image");
+                        try s.objectField("mimeType");
+                        try s.write(m.media_type);
+                        try s.objectField("data");
+                        try s.write(m.data);
+                        try s.endObject();
+                    },
+                }
+            }
+            try s.endArray();
+            try s.endObject();
+        },
+        .compaction_summary => |b| {
+            try s.beginObject();
+            try s.objectField("type");
+            try s.write("compactionSummary");
+            try s.objectField("text");
+            try s.write(b.text);
+            try s.endObject();
+        },
+    }
+}
+
+// =============================================================================
+// Parsing
+// =============================================================================
+
+pub const ParseError = error{
+    InvalidJson,
+    MissingField,
+    UnknownType,
+    UnknownRole,
+    UnknownBlockType,
+} || Allocator.Error;
+
+/// Parse one JSON line into a `FileEntry`. Caller owns all bytes.
+pub fn parseLine(allocator: Allocator, line: []const u8) ParseError!FileEntry {
+    var parsed = std.json.parseFromSlice(std.json.Value, allocator, line, .{}) catch {
+        return error.InvalidJson;
+    };
+    defer parsed.deinit();
+    return parseValue(allocator, parsed.value);
+}
+
+fn parseValue(allocator: Allocator, v: std.json.Value) ParseError!FileEntry {
+    if (v != .object) return error.InvalidJson;
+    const type_v = v.object.get("type") orelse return error.MissingField;
+    if (type_v != .string) return error.MissingField;
+    const t = type_v.string;
+    if (std.mem.eql(u8, t, "session")) {
+        return .{ .header = try parseHeaderFromObject(allocator, v.object) };
+    } else if (std.mem.eql(u8, t, "message")) {
+        return .{ .entry = .{ .message = try parseMessageEntry(allocator, v.object) } };
+    } else {
+        return error.UnknownType;
+    }
+}
+
+fn parseHeaderFromObject(allocator: Allocator, obj: std.json.ObjectMap) ParseError!SessionHeader {
+    const version: u32 = blk: {
+        if (obj.get("version")) |vv| {
+            if (vv == .integer) break :blk @intCast(vv.integer);
+        }
+        break :blk 1;
+    };
+    const id = try dupeStringField(allocator, obj, "id");
+    errdefer allocator.free(id);
+    const timestamp = try dupeStringField(allocator, obj, "timestamp");
+    errdefer allocator.free(timestamp);
+    const metadata: ?[]const u8 = blk: {
+        if (obj.get("metadata")) |mv| {
+            break :blk try std.json.Stringify.valueAlloc(allocator, mv, .{});
+        }
+        if (obj.get("cwd")) |cv| {
+            if (cv != .string) return error.MissingField;
+            const cwd_json = try std.json.Stringify.valueAlloc(allocator, cv, .{});
+            defer allocator.free(cwd_json);
+            break :blk try std.fmt.allocPrint(allocator, "{{\"cwd\":{s}}}", .{cwd_json});
+        }
+        break :blk null;
+    };
+    errdefer if (metadata) |m| allocator.free(m);
+    return .{
+        .version = version,
+        .id = id,
+        .timestamp = timestamp,
+        .metadata = metadata,
+    };
+}
+
+fn parseMessageEntry(allocator: Allocator, obj: std.json.ObjectMap) ParseError!MessageEntry {
+    const id = try dupeStringField(allocator, obj, "id");
+    errdefer allocator.free(id);
+    const timestamp = try dupeStringField(allocator, obj, "timestamp");
+    errdefer allocator.free(timestamp);
+    const parent_id: ?[]const u8 = blk: {
+        const pv = obj.get("parentId") orelse break :blk null;
+        if (pv == .null) break :blk null;
+        if (pv != .string) return error.MissingField;
+        break :blk try allocator.dupe(u8, pv.string);
+    };
+    errdefer if (parent_id) |p| allocator.free(p);
+
+    const stamp = try parseWireStamp(allocator, obj);
+    errdefer if (stamp) |st| st.deinit(allocator);
+
+    const msg_v = obj.get("message") orelse return error.MissingField;
+    if (msg_v != .object) return error.MissingField;
+    const msg = try parseDiskMessage(allocator, msg_v.object);
+
+    return .{
+        .base = .{ .id = id, .parent_id = parent_id, .timestamp = timestamp },
+        .stamp = stamp,
+        .message = msg,
+    };
+}
+
+/// Parse the wire-format provider stamp from a message entry object.
+/// Returns null when no `apiStyle` field is present (system entries).
+fn parseWireStamp(allocator: Allocator, obj: std.json.ObjectMap) ParseError!?WireStamp {
+    const style_v = obj.get("apiStyle") orelse return null;
+    if (style_v != .string) return null;
+    const api_style = std.meta.stringToEnum(APIStyle, style_v.string) orelse return error.MissingField;
+    const base_url = try dupeStringField(allocator, obj, "baseUrl");
+    errdefer allocator.free(base_url);
+    const model = try dupeStringField(allocator, obj, "model");
+    errdefer allocator.free(model);
+    // OpenAI: absent reasoning defaults to .default.
+    const reasoning: ReasoningEffort = blk: {
+        const rv = obj.get("reasoning") orelse break :blk .default;
+        if (rv != .string) break :blk .default;
+        break :blk std.meta.stringToEnum(ReasoningEffort, rv.string) orelse .default;
+    };
+    // Anthropic: absent fields default to the same values as the config defaults.
+    const thinking: Thinking = blk: {
+        const tv = obj.get("thinking") orelse break :blk .enabled;
+        if (tv != .string) break :blk .enabled;
+        break :blk std.meta.stringToEnum(Thinking, tv.string) orelse .enabled;
+    };
+    const effort: Effort = blk: {
+        const ev = obj.get("effort") orelse break :blk .medium;
+        if (ev != .string) break :blk .medium;
+        break :blk std.meta.stringToEnum(Effort, ev.string) orelse .medium;
+    };
+    const thinking_budget_tokens: ?u32 = blk: {
+        const bv = obj.get("thinkingBudgetTokens") orelse break :blk 32_000;
+        if (bv == .null) break :blk null;
+        if (bv != .integer) break :blk 32_000;
+        if (bv.integer < 0) break :blk 32_000;
+        break :blk @intCast(bv.integer);
+    };
+    const thinking_interleaved: bool = blk: {
+        const iv = obj.get("thinkingInterleaved") orelse break :blk false;
+        if (iv != .bool) break :blk false;
+        break :blk iv.bool;
+    };
+    return .{
+        .api_style = api_style,
+        .base_url = base_url,
+        .model = model,
+        .reasoning = reasoning,
+        .thinking = thinking,
+        .effort = effort,
+        .thinking_budget_tokens = thinking_budget_tokens,
+        .thinking_interleaved = thinking_interleaved,
+    };
+}
+
+fn parseDiskMessage(allocator: Allocator, obj: std.json.ObjectMap) ParseError!StoredMessage {
+    const role_v = obj.get("role") orelse return error.MissingField;
+    if (role_v != .string) return error.MissingField;
+    const role = std.meta.stringToEnum(StoredMessageRole, role_v.string) orelse return error.UnknownRole;
+
+    // `mode` is optional; absent defaults to `.append`. Unknown values are
+    // tolerated as `.append` rather than rejecting an otherwise-valid log.
+    const mode: StoredSystemMode = blk: {
+        const mv = obj.get("mode") orelse break :blk .append;
+        if (mv != .string) break :blk .append;
+        break :blk std.meta.stringToEnum(StoredSystemMode, mv.string) orelse .append;
+    };
+
+    const content_v = obj.get("content") orelse return error.MissingField;
+    if (content_v != .array) return error.MissingField;
+    var content_list = try std.ArrayList(StoredContentBlock).initCapacity(allocator, content_v.array.items.len);
+    errdefer {
+        for (content_list.items) |b| b.deinit(allocator);
+        content_list.deinit(allocator);
+    }
+    for (content_v.array.items) |item| {
+        if (item != .object) return error.UnknownBlockType;
+        const block = try parseDiskBlock(allocator, item.object);
+        try content_list.append(allocator, block);
+    }
+    const content = try content_list.toOwnedSlice(allocator);
+    errdefer {
+        for (content) |b| b.deinit(allocator);
+        allocator.free(content);
+    }
+
+    const stop_reason: ?[]const u8 = try dupeOptionalStringField(allocator, obj, "stopReason");
+    errdefer if (stop_reason) |s| allocator.free(s);
+    const metadata: ?[]const u8 = try dupeOptionalStringField(allocator, obj, "metadata");
+    errdefer if (metadata) |m| allocator.free(m);
+
+    var usage: ?Usage = null;
+    if (obj.get("usage")) |uv| {
+        if (uv == .object) {
+            usage = .{
+                .input = readU64(uv.object, "input"),
+                .output = readU64(uv.object, "output"),
+                .cache_read = readU64(uv.object, "cacheRead"),
+                .cache_write = readU64(uv.object, "cacheWrite"),
+                .reasoning = readU64(uv.object, "reasoning"),
+            };
+        }
+    }
+
+    return .{
+        .role = role,
+        .content = content,
+        .mode = mode,
+        .stop_reason = stop_reason,
+        .usage = usage,
+        .metadata = metadata,
+    };
+}
+
+fn parseDiskBlock(allocator: Allocator, obj: std.json.ObjectMap) ParseError!StoredContentBlock {
+    const type_v = obj.get("type") orelse return error.MissingField;
+    if (type_v != .string) return error.MissingField;
+    const t = type_v.string;
+    if (std.mem.eql(u8, t, "text")) {
+        const text = try dupeStringField(allocator, obj, "text");
+        return .{ .text = .{ .text = text } };
+    } else if (std.mem.eql(u8, t, "thinking")) {
+        const text = try dupeStringField(allocator, obj, "thinking");
+        errdefer allocator.free(text);
+        const sig = try dupeOptionalStringField(allocator, obj, "signature");
+        return .{ .thinking = .{ .thinking = text, .signature = sig } };
+    } else if (std.mem.eql(u8, t, "toolUse")) {
+        const id = try dupeStringField(allocator, obj, "id");
+        errdefer allocator.free(id);
+        const name = try dupeStringField(allocator, obj, "name");
+        errdefer allocator.free(name);
+        const input = try dupeStringField(allocator, obj, "input");
+        return .{ .tool_use = .{ .id = id, .name = name, .input = input } };
+    } else if (std.mem.eql(u8, t, "toolResult")) {
+        const tuid = try dupeStringField(allocator, obj, "toolUseId");
+        errdefer allocator.free(tuid);
+        const parts = try parseDiskResultParts(allocator, obj);
+        // Missing `isError` in older logs defaults to false.
+        const is_err = readBool(obj, "isError");
+        return .{ .tool_result = .{ .tool_use_id = tuid, .parts = parts, .is_error = is_err } };
+    } else if (std.mem.eql(u8, t, "compactionSummary")) {
+        const text = try dupeStringField(allocator, obj, "text");
+        return .{ .compaction_summary = .{ .text = text } };
+    } else {
+        return error.UnknownBlockType;
+    }
+}
+
+/// Parse the `parts` array of a `toolResult` disk block. Falls back to a
+/// legacy single `content` string field (older session logs) -> one text
+/// part. Each element is {type:"text",text} or {type:"image",mimeType,data}.
+fn parseDiskResultParts(allocator: Allocator, obj: std.json.ObjectMap) ParseError![]StoredResultPart {
+    var list: std.ArrayList(StoredResultPart) = .empty;
+    errdefer {
+        for (list.items) |p| p.deinit(allocator);
+        list.deinit(allocator);
+    }
+    const parts_v = obj.get("parts");
+    if (parts_v == null or parts_v.? == .null) {
+        // Legacy: a single `content` string.
+        const content = try dupeStringField(allocator, obj, "content");
+        try list.append(allocator, .{ .text = content });
+        return list.toOwnedSlice(allocator);
+    }
+    if (parts_v.? != .array) return error.MissingField;
+    for (parts_v.?.array.items) |item| {
+        if (item != .object) return error.MissingField;
+        const po = item.object;
+        const pt_v = po.get("type") orelse return error.MissingField;
+        if (pt_v != .string) return error.MissingField;
+        if (std.mem.eql(u8, pt_v.string, "text")) {
+            const text = try dupeStringField(allocator, po, "text");
+            try list.append(allocator, .{ .text = text });
+        } else if (std.mem.eql(u8, pt_v.string, "image")) {
+            const mt = try dupeStringField(allocator, po, "mimeType");
+            errdefer allocator.free(mt);
+            const data = try dupeStringField(allocator, po, "data");
+            try list.append(allocator, .{ .media = .{ .media_type = mt, .data = data } });
+        } else {
+            return error.UnknownBlockType;
+        }
+    }
+    return list.toOwnedSlice(allocator);
+}
+
+fn readBool(obj: std.json.ObjectMap, name: []const u8) bool {
+    const v = obj.get(name) orelse return false;
+    if (v != .bool) return false;
+    return v.bool;
+}
+
+fn readU64(obj: std.json.ObjectMap, name: []const u8) u64 {
+    const v = obj.get(name) orelse return 0;
+    if (v != .integer) return 0;
+    if (v.integer < 0) return 0;
+    return @intCast(v.integer);
+}
+
+fn dupeStringField(allocator: Allocator, obj: std.json.ObjectMap, name: []const u8) ParseError![]const u8 {
+    const v = obj.get(name) orelse return error.MissingField;
+    if (v != .string) return error.MissingField;
+    return try allocator.dupe(u8, v.string);
+}
+
+fn dupeOptionalStringField(allocator: Allocator, obj: std.json.ObjectMap, name: []const u8) ParseError!?[]const u8 {
+    const v = obj.get(name) orelse return null;
+    if (v == .null) return null;
+    if (v != .string) return error.MissingField;
+    return try allocator.dupe(u8, v.string);
+}
+
+// =============================================================================
+// Bridge between in-memory and on-disk content blocks
+// =============================================================================
+
+/// Convert an in-memory `ContentBlock` to a `StoredContentBlock`. All strings
+/// are duplicated; the source block remains untouched and the resulting
+/// disk block is independently owned.
+pub fn contentBlockToDisk(
+    allocator: Allocator,
+    block: conversation.ContentBlock,
+) !StoredContentBlock {
+    switch (block) {
+        .Text => |tb| {
+            const text = try allocator.dupe(u8, tb.items);
+            return .{ .text = .{ .text = text } };
+        },
+        .Thinking => |tb| {
+            const text = try allocator.dupe(u8, tb.text.items);
+            errdefer allocator.free(text);
+            const sig: ?[]const u8 = if (tb.signature) |s| try allocator.dupe(u8, s) else null;
+            return .{ .thinking = .{ .thinking = text, .signature = sig } };
+        },
+        .ToolUse => |tu| {
+            const id = try allocator.dupe(u8, tu.id);
+            errdefer allocator.free(id);
+            const name = try allocator.dupe(u8, tu.name);
+            errdefer allocator.free(name);
+            const input = try allocator.dupe(u8, tu.input.items);
+            return .{ .tool_use = .{ .id = id, .name = name, .input = input } };
+        },
+        .ToolResult => |tr| {
+            const tuid = try allocator.dupe(u8, tr.tool_use_id);
+            errdefer allocator.free(tuid);
+            var parts: std.ArrayList(StoredResultPart) = .empty;
+            errdefer {
+                for (parts.items) |p| p.deinit(allocator);
+                parts.deinit(allocator);
+            }
+            try parts.ensureTotalCapacity(allocator, tr.parts.items.len);
+            for (tr.parts.items) |src| {
+                switch (src) {
+                    .text => |tb| parts.appendAssumeCapacity(.{ .text = try allocator.dupe(u8, tb.items) }),
+                    .media => |m| {
+                        const mt = try allocator.dupe(u8, m.media_type);
+                        errdefer allocator.free(mt);
+                        const data = try allocator.dupe(u8, m.data.items);
+                        parts.appendAssumeCapacity(.{ .media = .{ .media_type = mt, .data = data } });
+                    },
+                }
+            }
+            return .{ .tool_result = .{
+                .tool_use_id = tuid,
+                .parts = try parts.toOwnedSlice(allocator),
+                .is_error = tr.is_error,
+            } };
+        },
+        // A `.System` block becomes a disk text block; its mode rides on
+        // the enclosing `StoredMessage.mode` (set by the session manager),
+        // not on the block itself.
+        .System => |sb| {
+            const text = try allocator.dupe(u8, sb.text.items);
+            return .{ .text = .{ .text = text } };
+        },
+        .CompactionSummary => |cs| {
+            const text = try allocator.dupe(u8, cs.text.items);
+            return .{ .compaction_summary = .{ .text = text } };
+        },
+    }
+}
+
+/// Convert a `StoredContentBlock` to an in-memory `ContentBlock`. Allocates
+/// fresh owned buffers for every string field. The returned block is
+/// independently owned.
+pub fn diskContentBlockToInternal(
+    allocator: Allocator,
+    block: StoredContentBlock,
+) !conversation.ContentBlock {
+    switch (block) {
+        .text => |b| {
+            const tb = try conversation.textualBlockFromSlice(allocator, b.text);
+            return .{ .Text = tb };
+        },
+        .thinking => |b| {
+            const tb = try conversation.textualBlockFromSlice(allocator, b.thinking);
+            errdefer {
+                var mut = tb;
+                mut.deinit(allocator);
+            }
+            const sig: ?[]const u8 = if (b.signature) |s| try allocator.dupe(u8, s) else null;
+            return .{ .Thinking = .{ .text = tb, .signature = sig } };
+        },
+        .tool_use => |b| {
+            const id = try allocator.dupe(u8, b.id);
+            errdefer allocator.free(id);
+            const name = try allocator.dupe(u8, b.name);
+            errdefer allocator.free(name);
+            const input = try conversation.textualBlockFromSlice(allocator, b.input);
+            return .{ .ToolUse = .{ .id = id, .name = name, .input = input } };
+        },
+        .tool_result => |b| {
+            const tuid = try allocator.dupe(u8, b.tool_use_id);
+            errdefer allocator.free(tuid);
+            var parts: std.ArrayList(conversation.ResultPartStored) = .empty;
+            errdefer {
+                for (parts.items) |*p| p.deinit(allocator);
+                parts.deinit(allocator);
+            }
+            try parts.ensureTotalCapacity(allocator, b.parts.len);
+            for (b.parts) |src| {
+                switch (src) {
+                    .text => |t| parts.appendAssumeCapacity(.{ .text = try conversation.textualBlockFromSlice(allocator, t) }),
+                    .media => |m| {
+                        const mt = try allocator.dupe(u8, m.media_type);
+                        errdefer allocator.free(mt);
+                        const data = try conversation.textualBlockFromSlice(allocator, m.data);
+                        parts.appendAssumeCapacity(.{ .media = .{ .media_type = mt, .data = data } });
+                    },
+                }
+            }
+            return .{ .ToolResult = .{ .tool_use_id = tuid, .parts = parts, .is_error = b.is_error } };
+        },
+        .compaction_summary => |b| {
+            const tb = try conversation.textualBlockFromSlice(allocator, b.text);
+            return .{ .CompactionSummary = .{ .text = tb } };
+        },
+    }
+}
+
+// =============================================================================
+// Tests
+// =============================================================================
+
+const testing = std.testing;
+
+fn dupe(allocator: Allocator, s: []const u8) ![]const u8 {
+    return try allocator.dupe(u8, s);
+}
+
+test "serialize/parse header round-trip" {
+    const a = testing.allocator;
+    const header: SessionHeader = .{
+        .version = 1,
+        .id = try dupe(a, "019dc5ba-53f6-71a5-ab8f-b1f8709c2572"),
+        .timestamp = try dupe(a, "2026-04-25T17:40:15.990Z"),
+        .metadata = try dupe(a, "{\"cwd\":\"/Users/travis/Code/pantograph\"}"),
+    };
+    defer header.deinit(a);
+
+    const line = try serializeHeader(a, header);
+    defer a.free(line);
+
+    var fe = try parseLine(a, line);
+    defer fe.deinit(a);
+    try testing.expect(fe == .header);
+    try testing.expectEqual(@as(u32, 1), fe.header.version);
+    try testing.expectEqualStrings(header.id, fe.header.id);
+    try testing.expectEqualStrings(header.metadata.?, fe.header.metadata.?);
+}
+
+test "serialize/parse user message entry round-trip (with provider/model stamp)" {
+    const a = testing.allocator;
+
+    var content = try a.alloc(StoredContentBlock, 1);
+    content[0] = .{ .text = .{ .text = try dupe(a, "hello world") } };
+
+    const entry: SessionEntry = .{ .message = .{
+        .base = .{
+            .id = try dupe(a, "a1b2c3d4"),
+            .parent_id = try dupe(a, "00000000"),
+            .timestamp = try dupe(a, "2026-04-25T17:40:16.000Z"),
+        },
+        .stamp = .{
+            .api_style = .openai_chat,
+            .base_url = try dupe(a, "https://api.openai.com/v1"),
+            .model = try dupe(a, "gpt-4o"),
+            .reasoning = .high,
+        },
+        .message = .{
+            .role = .user,
+            .content = content,
+        },
+    } };
+    defer entry.deinit(a);
+
+    const line = try serializeEntry(a, entry);
+    defer a.free(line);
+
+    var fe = try parseLine(a, line);
+    defer fe.deinit(a);
+    try testing.expect(fe == .entry);
+    const got = fe.entry.message;
+    try testing.expectEqualStrings("a1b2c3d4", got.base.id);
+    try testing.expectEqualStrings("00000000", got.base.parent_id.?);
+    try testing.expectEqual(APIStyle.openai_chat, got.stamp.?.api_style);
+    try testing.expectEqualStrings("https://api.openai.com/v1", got.stamp.?.base_url);
+    try testing.expectEqualStrings("gpt-4o", got.stamp.?.model);
+    try testing.expectEqual(ReasoningEffort.high, got.stamp.?.reasoning);
+    try testing.expectEqual(StoredMessageRole.user, got.message.role);
+    try testing.expectEqual(@as(usize, 1), got.message.content.len);
+    try testing.expectEqualStrings("hello world", got.message.content[0].text.text);
+}
+
+test "serialize/parse assistant message entry with metadata" {
+    const a = testing.allocator;
+
+    var content = try a.alloc(StoredContentBlock, 3);
+    content[0] = .{ .thinking = .{
+        .thinking = try dupe(a, "let me think"),
+        .signature = try dupe(a, "sig-xyz"),
+    } };
+    content[1] = .{ .text = .{ .text = try dupe(a, "I'll check.") } };
+    content[2] = .{ .tool_use = .{
+        .id = try dupe(a, "tool_abc"),
+        .name = try dupe(a, "bash"),
+        .input = try dupe(a, "{\"command\":\"ls\"}"),
+    } };
+
+    const entry: SessionEntry = .{ .message = .{
+        .base = .{
+            .id = try dupe(a, "b2c3d4e5"),
+            .parent_id = try dupe(a, "a1b2c3d4"),
+            .timestamp = try dupe(a, "2026-04-25T17:40:17.000Z"),
+        },
+        .stamp = .{
+            .api_style = .anthropic_messages,
+            .base_url = try dupe(a, "https://api.anthropic.com"),
+            .model = try dupe(a, "claude-sonnet-4-20250514"),
+        },
+        .message = .{
+            .role = .assistant,
+            .content = content,
+            .stop_reason = try dupe(a, "toolUse"),
+            .usage = .{ .input = 1500, .output = 85 },
+            .metadata = try dupe(a, "{\"k\":1}"),
+        },
+    } };
+    defer entry.deinit(a);
+
+    const line = try serializeEntry(a, entry);
+    defer a.free(line);
+
+    var fe = try parseLine(a, line);
+    defer fe.deinit(a);
+    const got = fe.entry.message;
+    try testing.expectEqual(StoredMessageRole.assistant, got.message.role);
+    try testing.expectEqual(@as(usize, 3), got.message.content.len);
+    try testing.expectEqualStrings("let me think", got.message.content[0].thinking.thinking);
+    try testing.expectEqualStrings("sig-xyz", got.message.content[0].thinking.signature.?);
+    try testing.expectEqualStrings("bash", got.message.content[2].tool_use.name);
+    try testing.expectEqualStrings("{\"command\":\"ls\"}", got.message.content[2].tool_use.input);
+    try testing.expectEqualStrings("anthropic", @tagName(got.stamp.?.api_style)[0..9]);
+    try testing.expectEqualStrings("toolUse", got.message.stop_reason.?);
+    try testing.expectEqualStrings("{\"k\":1}", got.message.metadata.?);
+    try testing.expect(got.message.usage != null);
+    try testing.expectEqual(@as(u64, 1500), got.message.usage.?.input);
+    try testing.expectEqual(@as(u64, 85), got.message.usage.?.output);
+}
+
+test "serialize/parse tool result message entry" {
+    const a = testing.allocator;
+
+    var content = try a.alloc(StoredContentBlock, 1);
+    var trp = try a.alloc(StoredResultPart, 1);
+    trp[0] = .{ .text = try dupe(a, "file1.txt\nfile2.txt") };
+    content[0] = .{ .tool_result = .{
+        .tool_use_id = try dupe(a, "tool_abc"),
+        .parts = trp,
+    } };
+
+    const entry: SessionEntry = .{ .message = .{
+        .base = .{
+            .id = try dupe(a, "c3d4e5f6"),
+            .parent_id = try dupe(a, "b2c3d4e5"),
+            .timestamp = try dupe(a, "2026-04-25T17:40:18.000Z"),
+        },
+        .stamp = .{
+            .api_style = .anthropic_messages,
+            .base_url = try dupe(a, "https://api.anthropic.com"),
+            .model = try dupe(a, "claude-sonnet-4-20250514"),
+        },
+        .message = .{
+            .role = .user,
+            .content = content,
+        },
+    } };
+    defer entry.deinit(a);
+
+    const line = try serializeEntry(a, entry);
+    defer a.free(line);
+
+    var fe = try parseLine(a, line);
+    defer fe.deinit(a);
+    const got = fe.entry.message;
+    try testing.expectEqual(StoredMessageRole.user, got.message.role);
+    try testing.expectEqualStrings("tool_abc", got.message.content[0].tool_result.tool_use_id);
+    try testing.expectEqual(@as(usize, 1), got.message.content[0].tool_result.parts.len);
+    try testing.expectEqualStrings("file1.txt\nfile2.txt", got.message.content[0].tool_result.parts[0].text);
+    try testing.expectEqual(APIStyle.anthropic_messages, got.stamp.?.api_style);
+    // Unset is_error defaults to false and serializes without the field.
+    try testing.expect(!got.message.content[0].tool_result.is_error);
+    try testing.expect(std.mem.indexOf(u8, line, "isError") == null);
+}
+
+test "serialize/parse tool result preserves is_error = true" {
+    const a = testing.allocator;
+
+    var content = try a.alloc(StoredContentBlock, 1);
+    var trp = try a.alloc(StoredResultPart, 1);
+    trp[0] = .{ .text = try dupe(a, "file not found") };
+    content[0] = .{ .tool_result = .{
+        .tool_use_id = try dupe(a, "tool_err"),
+        .parts = trp,
+        .is_error = true,
+    } };
+
+    const entry: SessionEntry = .{ .message = .{
+        .base = .{
+            .id = try dupe(a, "e1"),
+            .parent_id = try dupe(a, "e0"),
+            .timestamp = try dupe(a, "2026-04-25T17:40:18.000Z"),
+        },
+        .stamp = .{
+            .api_style = .anthropic_messages,
+            .base_url = try dupe(a, "https://api.anthropic.com"),
+            .model = try dupe(a, "claude-sonnet-4-20250514"),
+        },
+        .message = .{ .role = .user, .content = content },
+    } };
+    defer entry.deinit(a);
+
+    const line = try serializeEntry(a, entry);
+    defer a.free(line);
+    try testing.expect(std.mem.indexOf(u8, line, "\"isError\":true") != null);
+
+    var fe = try parseLine(a, line);
+    defer fe.deinit(a);
+    try testing.expect(fe.entry.message.message.content[0].tool_result.is_error);
+}
+
+test "parse tool result without isError defaults to false" {
+    const a = testing.allocator;
+    // A legacy line predating the is_error field.
+    const line =
+        \\{"type":"message","id":"x","parentId":"y","timestamp":"t","provider":"anthropic","model":"m","message":{"role":"user","content":[{"type":"toolResult","toolUseId":"t1","parts":[{"type":"text","text":"ok"}]}]}}
+    ;
+    var fe = try parseLine(a, line);
+    defer fe.deinit(a);
+    try testing.expect(!fe.entry.message.message.content[0].tool_result.is_error);
+}
+
+test "serialize/parse tool result with text + image part round-trips" {
+    const a = testing.allocator;
+
+    var content = try a.alloc(StoredContentBlock, 1);
+    var trp = try a.alloc(StoredResultPart, 2);
+    trp[0] = .{ .text = try dupe(a, "here is the image") };
+    trp[1] = .{ .media = .{
+        .media_type = try dupe(a, "image/png"),
+        .data = try dupe(a, "iVBORw0KGgo="),
+    } };
+    content[0] = .{ .tool_result = .{
+        .tool_use_id = try dupe(a, "tool_img"),
+        .parts = trp,
+    } };
+
+    const entry: SessionEntry = .{ .message = .{
+        .base = .{
+            .id = try dupe(a, "img00001"),
+            .parent_id = try dupe(a, "img00000"),
+            .timestamp = try dupe(a, "2026-04-25T17:40:18.000Z"),
+        },
+        .stamp = .{
+            .api_style = .anthropic_messages,
+            .base_url = try dupe(a, "https://api.anthropic.com"),
+            .model = try dupe(a, "claude-sonnet-4-20250514"),
+        },
+        .message = .{ .role = .user, .content = content },
+    } };
+    defer entry.deinit(a);
+
+    const line = try serializeEntry(a, entry);
+    defer a.free(line);
+
+    var fe = try parseLine(a, line);
+    defer fe.deinit(a);
+    const tr = fe.entry.message.message.content[0].tool_result;
+    try testing.expectEqualStrings("tool_img", tr.tool_use_id);
+    try testing.expectEqual(@as(usize, 2), tr.parts.len);
+    try testing.expectEqualStrings("here is the image", tr.parts[0].text);
+    try testing.expectEqualStrings("image/png", tr.parts[1].media.media_type);
+    try testing.expectEqualStrings("iVBORw0KGgo=", tr.parts[1].media.data);
+}
+
+test "system message mode round-trips; absent mode defaults to append" {
+    const a = testing.allocator;
+
+    // replace-mode system entry round-trips.
+    {
+        var content = try a.alloc(StoredContentBlock, 1);
+        content[0] = .{ .text = .{ .text = try dupe(a, "fresh seed") } };
+        const entry: SessionEntry = .{ .message = .{
+            .base = .{
+                .id = try dupe(a, "aabbccdd"),
+                .parent_id = null,
+                .timestamp = try dupe(a, "2026-04-25T17:40:00Z"),
+            },
+            .message = .{
+                .role = .system,
+                .content = content,
+                .mode = .replace,
+            },
+        } };
+        defer entry.deinit(a);
+
+        const line = try serializeEntry(a, entry);
+        defer a.free(line);
+        try testing.expect(std.mem.indexOf(u8, line, "\"mode\":\"replace\"") != null);
+
+        var fe = try parseLine(a, line);
+        defer fe.deinit(a);
+        try testing.expectEqual(StoredSystemMode.replace, fe.entry.message.message.mode);
+    }
+
+    // A legacy system entry with no `mode` parses back as append.
+    {
+        const line =
+            \\{"type":"message","id":"abcdefab","parentId":null,"timestamp":"2026-04-25T17:40:00Z","message":{"role":"system","content":[{"type":"text","text":"hi"}]}}
+        ;
+        var fe = try parseLine(a, line);
+        defer fe.deinit(a);
+        try testing.expectEqual(StoredSystemMode.append, fe.entry.message.message.mode);
+    }
+}
+
+test "parse: null parentId is handled" {
+    const a = testing.allocator;
+    const line =
+        \\{"type":"message","id":"abcdefab","parentId":null,"timestamp":"2026-04-25T17:40:00Z","message":{"role":"system","content":[{"type":"text","text":"hi"}]}}
+    ;
+    var fe = try parseLine(a, line);
+    defer fe.deinit(a);
+    try testing.expect(fe.entry.message.base.parent_id == null);
+}
+
+test "parse: malformed JSON is reported" {
+    const a = testing.allocator;
+    try testing.expectError(error.InvalidJson, parseLine(a, "not json"));
+    try testing.expectError(error.InvalidJson, parseLine(a, "{\"type\":\"message\""));
+}
+
+test "parse: unknown entry type is reported" {
+    const a = testing.allocator;
+    const line =
+        \\{"type":"future_entry","id":"abcdefab","parentId":null,"timestamp":"2026-04-25T17:40:00Z"}
+    ;
+    try testing.expectError(error.UnknownType, parseLine(a, line));
+}
+
+test "contentBlockToDisk: Text round-trips via in-memory" {
+    const a = testing.allocator;
+
+    var tb = try conversation.textualBlockFromSlice(a, "hello");
+    defer tb.deinit(a);
+    const block: conversation.ContentBlock = .{ .Text = tb };
+
+    const disk = try contentBlockToDisk(a, block);
+    defer disk.deinit(a);
+    try testing.expectEqualStrings("hello", disk.text.text);
+}
+
+test "diskContentBlockToInternal: ToolUse preserves id/name/input" {
+    const a = testing.allocator;
+
+    const disk: StoredContentBlock = .{ .tool_use = .{
+        .id = try a.dupe(u8, "tu_1"),
+        .name = try a.dupe(u8, "bash"),
+        .input = try a.dupe(u8, "{\"command\":\"ls\"}"),
+    } };
+    defer disk.deinit(a);
+
+    var inmem = try diskContentBlockToInternal(a, disk);
+    defer inmem.deinit(a);
+    try testing.expectEqualStrings("tu_1", inmem.ToolUse.id);
+    try testing.expectEqualStrings("bash", inmem.ToolUse.name);
+    try testing.expectEqualStrings("{\"command\":\"ls\"}", inmem.ToolUse.input.items);
+}
+
+test "Usage: all five fields round-trip; zero-valued fields omitted from JSON" {
+    const a = testing.allocator;
+
+    var content = try a.alloc(StoredContentBlock, 1);
+    content[0] = .{ .text = .{ .text = try dupe(a, "hi") } };
+
+    const entry: SessionEntry = .{ .message = .{
+        .base = .{
+            .id = try dupe(a, "deadbeef"),
+            .parent_id = null,
+            .timestamp = try dupe(a, "2026-04-25T17:40:17.000Z"),
+        },
+        .message = .{
+            .role = .assistant,
+            .content = content,
+            .stop_reason = try dupe(a, "stop"),
+            .usage = .{
+                .input = 100,
+                .output = 50,
+                .cache_read = 800,
+                .cache_write = 200,
+                .reasoning = 30,
+            },
+        },
+    } };
+    defer entry.deinit(a);
+
+    const line = try serializeEntry(a, entry);
+    defer a.free(line);
+
+    // Every non-zero field should appear in the serialized JSON.
+    try testing.expect(std.mem.indexOf(u8, line, "\"input\":100") != null);
+    try testing.expect(std.mem.indexOf(u8, line, "\"output\":50") != null);
+    try testing.expect(std.mem.indexOf(u8, line, "\"cacheRead\":800") != null);
+    try testing.expect(std.mem.indexOf(u8, line, "\"cacheWrite\":200") != null);
+    try testing.expect(std.mem.indexOf(u8, line, "\"reasoning\":30") != null);
+
+    var fe = try parseLine(a, line);
+    defer fe.deinit(a);
+    const u = fe.entry.message.message.usage.?;
+    try testing.expectEqual(@as(u64, 100), u.input);
+    try testing.expectEqual(@as(u64, 50), u.output);
+    try testing.expectEqual(@as(u64, 800), u.cache_read);
+    try testing.expectEqual(@as(u64, 200), u.cache_write);
+    try testing.expectEqual(@as(u64, 30), u.reasoning);
+}
+
+test "Usage: zero-valued auxiliary fields are omitted but parse back as 0" {
+    const a = testing.allocator;
+
+    var content = try a.alloc(StoredContentBlock, 1);
+    content[0] = .{ .text = .{ .text = try dupe(a, "hi") } };
+
+    const entry: SessionEntry = .{ .message = .{
+        .base = .{
+            .id = try dupe(a, "deadbeef"),
+            .parent_id = null,
+            .timestamp = try dupe(a, "2026-04-25T17:40:17.000Z"),
+        },
+        .message = .{
+            .role = .assistant,
+            .content = content,
+            .usage = .{ .input = 100, .output = 50 },
+        },
+    } };
+    defer entry.deinit(a);
+
+    const line = try serializeEntry(a, entry);
+    defer a.free(line);
+
+    try testing.expect(std.mem.indexOf(u8, line, "cacheRead") == null);
+    try testing.expect(std.mem.indexOf(u8, line, "cacheWrite") == null);
+    try testing.expect(std.mem.indexOf(u8, line, "reasoning") == null);
+
+    var fe = try parseLine(a, line);
+    defer fe.deinit(a);
+    const u = fe.entry.message.message.usage.?;
+    try testing.expectEqual(@as(u64, 0), u.cache_read);
+    try testing.expectEqual(@as(u64, 0), u.cache_write);
+    try testing.expectEqual(@as(u64, 0), u.reasoning);
+}
+
+test "diskContentBlockToInternal: Thinking preserves signature" {
+    const a = testing.allocator;
+
+    const disk: StoredContentBlock = .{ .thinking = .{
+        .thinking = try a.dupe(u8, "reasoning..."),
+        .signature = try a.dupe(u8, "sig123"),
+    } };
+    defer disk.deinit(a);
+
+    var inmem = try diskContentBlockToInternal(a, disk);
+    defer inmem.deinit(a);
+    try testing.expectEqualStrings("reasoning...", inmem.Thinking.text.items);
+    try testing.expectEqualStrings("sig123", inmem.Thinking.signature.?);
+}
+
+test "compactionSummary block round-trips through serialize/parse" {
+    const a = testing.allocator;
+
+    var content = try a.alloc(StoredContentBlock, 1);
+    content[0] = .{ .compaction_summary = .{ .text = try dupe(a, "earlier history summary") } };
+
+    const entry: SessionEntry = .{ .message = .{
+        .base = .{
+            .id = try dupe(a, "cafef00d"),
+            .parent_id = null,
+            .timestamp = try dupe(a, "2026-04-25T17:40:00Z"),
+        },
+        .message = .{ .role = .user, .content = content },
+    } };
+    defer entry.deinit(a);
+
+    const line = try serializeEntry(a, entry);
+    defer a.free(line);
+    try testing.expect(std.mem.indexOf(u8, line, "\"type\":\"compactionSummary\"") != null);
+
+    var fe = try parseLine(a, line);
+    defer fe.deinit(a);
+    const got = fe.entry.message;
+    try testing.expectEqual(StoredMessageRole.user, got.message.role);
+    try testing.expectEqualStrings("earlier history summary", got.message.content[0].compaction_summary.text);
+}
+
+test "compactionSummary bridges in-memory <-> disk both directions" {
+    const a = testing.allocator;
+
+    // in-memory -> disk
+    const tb = try conversation.textualBlockFromSlice(a, "S1");
+    const block: conversation.ContentBlock = .{ .CompactionSummary = .{ .text = tb } };
+    defer {
+        var mut = block;
+        mut.deinit(a);
+    }
+    const disk = try contentBlockToDisk(a, block);
+    defer disk.deinit(a);
+    try testing.expectEqualStrings("S1", disk.compaction_summary.text);
+
+    // disk -> in-memory
+    var inmem = try diskContentBlockToInternal(a, disk);
+    defer inmem.deinit(a);
+    try testing.expectEqualStrings("S1", inmem.CompactionSummary.text.items);
+}
+
+test "WireStamp: Anthropic non-default thinking fields round-trip" {
+    const a = testing.allocator;
+
+    var content = try a.alloc(StoredContentBlock, 1);
+    content[0] = .{ .text = .{ .text = try dupe(a, "hi") } };
+
+    const entry: SessionEntry = .{ .message = .{
+        .base = .{
+            .id = try dupe(a, "aa000001"),
+            .parent_id = null,
+            .timestamp = try dupe(a, "2026-06-01T00:00:00Z"),
+        },
+        .stamp = .{
+            .api_style = .anthropic_messages,
+            .base_url = try dupe(a, "https://api.anthropic.com"),
+            .model = try dupe(a, "claude-opus-4-8"),
+            .thinking = .adaptive,
+            .effort = .high,
+            .thinking_budget_tokens = null,
+            .thinking_interleaved = true,
+        },
+        .message = .{ .role = .user, .content = content },
+    } };
+    defer entry.deinit(a);
+
+    const line = try serializeEntry(a, entry);
+    defer a.free(line);
+
+    // Non-default fields must appear in the serialized line.
+    try testing.expect(std.mem.indexOf(u8, line, "\"thinking\":\"adaptive\"") != null);
+    try testing.expect(std.mem.indexOf(u8, line, "\"effort\":\"high\"") != null);
+    try testing.expect(std.mem.indexOf(u8, line, "\"thinkingBudgetTokens\":null") != null);
+    try testing.expect(std.mem.indexOf(u8, line, "\"thinkingInterleaved\":true") != null);
+
+    var fe = try parseLine(a, line);
+    defer fe.deinit(a);
+    const got = fe.entry.message.stamp.?;
+    try testing.expectEqual(APIStyle.anthropic_messages, got.api_style);
+    try testing.expectEqual(Thinking.adaptive, got.thinking);
+    try testing.expectEqual(Effort.high, got.effort);
+    try testing.expectEqual(@as(?u32, null), got.thinking_budget_tokens);
+    try testing.expectEqual(true, got.thinking_interleaved);
+    // reasoning carries its default (unused for Anthropic)
+    try testing.expectEqual(ReasoningEffort.default, got.reasoning);
+}
+
+test "WireStamp: Anthropic stamp with all-default thinking fields omits non-essential keys" {
+    const a = testing.allocator;
+
+    var content = try a.alloc(StoredContentBlock, 1);
+    content[0] = .{ .text = .{ .text = try dupe(a, "hi") } };
+
+    const entry: SessionEntry = .{ .message = .{
+        .base = .{
+            .id = try dupe(a, "bb000002"),
+            .parent_id = null,
+            .timestamp = try dupe(a, "2026-06-01T00:00:00Z"),
+        },
+        .stamp = .{
+            .api_style = .anthropic_messages,
+            .base_url = try dupe(a, "https://api.anthropic.com"),
+            .model = try dupe(a, "claude-haiku-4-5"),
+            // All defaults: thinking=.enabled, effort=.medium,
+            // thinking_budget_tokens=32_000, thinking_interleaved=false
+        },
+        .message = .{ .role = .user, .content = content },
+    } };
+    defer entry.deinit(a);
+
+    const line = try serializeEntry(a, entry);
+    defer a.free(line);
+
+    // Default-valued fields should be omitted (keeps logs compact).
+    try testing.expect(std.mem.indexOf(u8, line, "thinking") == null);
+    try testing.expect(std.mem.indexOf(u8, line, "effort") == null);
+    try testing.expect(std.mem.indexOf(u8, line, "thinkingInterleaved") == null);
+    // thinkingBudgetTokens=32_000 is the default, should be omitted too.
+    try testing.expect(std.mem.indexOf(u8, line, "thinkingBudgetTokens") == null);
+
+    // Round-trip: all defaults parse back correctly.
+    var fe = try parseLine(a, line);
+    defer fe.deinit(a);
+    const got = fe.entry.message.stamp.?;
+    try testing.expectEqual(Thinking.enabled, got.thinking);
+    try testing.expectEqual(Effort.medium, got.effort);
+    try testing.expectEqual(@as(?u32, 32_000), got.thinking_budget_tokens);
+    try testing.expectEqual(false, got.thinking_interleaved);
+}
+
+test "WireStamp: legacy Anthropic stamp (no thinking fields) parses with defaults" {
+    // Simulate a session log written before thinking fields were added.
+    const a = testing.allocator;
+    const line =
+        \\{"type":"message","id":"cc000003","parentId":null,"timestamp":"2026-06-01T00:00:00Z","apiStyle":"anthropic_messages","baseUrl":"https://api.anthropic.com","model":"claude-3-7-sonnet","message":{"role":"user","content":[{"type":"text","text":"hi"}]}}
+    ;
+    var fe = try parseLine(a, line);
+    defer fe.deinit(a);
+    const got = fe.entry.message.stamp.?;
+    try testing.expectEqual(APIStyle.anthropic_messages, got.api_style);
+    try testing.expectEqual(Thinking.enabled, got.thinking);
+    try testing.expectEqual(Effort.medium, got.effort);
+    try testing.expectEqual(@as(?u32, 32_000), got.thinking_budget_tokens);
+    try testing.expectEqual(false, got.thinking_interleaved);
+}
+
+test "WireStamp: OpenAI stamp is unchanged by Anthropic fields" {
+    const a = testing.allocator;
+
+    var content = try a.alloc(StoredContentBlock, 1);
+    content[0] = .{ .text = .{ .text = try dupe(a, "hi") } };
+
+    const entry: SessionEntry = .{ .message = .{
+        .base = .{
+            .id = try dupe(a, "dd000004"),
+            .parent_id = null,
+            .timestamp = try dupe(a, "2026-06-01T00:00:00Z"),
+        },
+        .stamp = .{
+            .api_style = .openai_chat,
+            .base_url = try dupe(a, "https://api.openai.com/v1"),
+            .model = try dupe(a, "gpt-4o"),
+            .reasoning = .high,
+        },
+        .message = .{ .role = .user, .content = content },
+    } };
+    defer entry.deinit(a);
+
+    const line = try serializeEntry(a, entry);
+    defer a.free(line);
+
+    // Anthropic fields should not appear for an OpenAI stamp.
+    try testing.expect(std.mem.indexOf(u8, line, "thinking") == null);
+    try testing.expect(std.mem.indexOf(u8, line, "effort") == null);
+    try testing.expect(std.mem.indexOf(u8, line, "thinkingBudget") == null);
+    try testing.expect(std.mem.indexOf(u8, line, "thinkingInterleaved") == null);
+    // reasoning=high should be present
+    try testing.expect(std.mem.indexOf(u8, line, "\"reasoning\":\"high\"") != null);
+
+    var fe = try parseLine(a, line);
+    defer fe.deinit(a);
+    const got = fe.entry.message.stamp.?;
+    try testing.expectEqual(APIStyle.openai_chat, got.api_style);
+    try testing.expectEqual(ReasoningEffort.high, got.reasoning);
+}