initial commit, moved libpanto over from the pantograph repo

1 files changed, 133 insertions, 0 deletions

diff --git a/src/turn_persist.zig b/src/turn_persist.zig
new file mode 100644
index 0000000..6d260c8
--- /dev/null
+++ b/src/turn_persist.zig
@@ -0,0 +1,133 @@
+//! Turn → session-log persistence: map in-memory `Conversation` messages
+//! to rich `PersistentMessage` write records and append them through a
+//! `Session` handle.
+//!
+//! This logic lives in `libpanto` and is called by the `Agent` itself, so
+//! every embedder gets persistence for free. The functions here are
+//! stateless helpers over a `Session`; the agent owns the store and the
+//! conversation.
+//!
+//! The write record is **maximalist** (full wire identity + usage + the
+//! entire current conversation + the offered tool set). The library offers
+//! it all on every append; each store keeps what it wants. `PersistentMessage`
+//! borrows the in-memory `Message` directly — no disk conversion happens
+//! here; the store does its own serialization.
+//!
+//! Per-message usage is read directly off `Message.usage`.
+
+const std = @import("std");
+const Allocator = std.mem.Allocator;
+
+const conversation = @import("conversation.zig");
+const session_store = @import("session_store.zig");
+
+const PersistentMessage = session_store.PersistentMessage;
+const WireIdentity = session_store.WireIdentity;
+const ToolDecl = session_store.ToolDecl;
+const Session = session_store.Session;
+
+/// Persist every conversation message at index `>= start_index` through
+/// `session` as a single atomic batch.
+///
+/// Each `PersistentMessage` borrows the in-memory `Message`, the full
+/// current conversation, and `tools` (the offered tool set) — all owned by
+/// the caller and valid for the duration of the call. The wire `identity`
+/// is stamped on every message; the store decides per-role what to keep
+/// (the FS store drops the stamp on system entries).
+///
+/// An assistant message carrying a ToolUse with no following matching
+/// ToolResult is skipped (a dangling tool call from an interrupted turn);
+/// persisting it would make the log un-replayable.
+pub fn persistTurn(
+    alloc: Allocator,
+    session: *Session,
+    conv: *conversation.Conversation,
+    start_index: usize,
+    identity: WireIdentity,
+    tools: []const ToolDecl,
+) !void {
+    return persistRange(alloc, session, conv, start_index, conv.messages.items.len, identity, tools);
+}
+
+/// Persist conversation messages in `[start_index, end_index)`. Like
+/// `persistTurn` but with an explicit upper bound, so an incremental flush can
+/// exclude a trailing not-yet-coherent message (a dangling tool call awaiting
+/// its results) while still committing everything before it.
+pub fn persistRange(
+    alloc: Allocator,
+    session: *Session,
+    conv: *conversation.Conversation,
+    start_index: usize,
+    end_index: usize,
+    identity: WireIdentity,
+    tools: []const ToolDecl,
+) !void {
+    var batch: std.ArrayList(PersistentMessage) = .empty;
+    defer batch.deinit(alloc);
+
+    const all_messages = conv.messages.items;
+    var i = start_index;
+    while (i < end_index) : (i += 1) {
+        const msg = &all_messages[i];
+        if (msg.role == .assistant and hasToolUseWithoutFollowingResults(conv, i)) {
+            continue;
+        }
+        // Stamp the producing identity once, on first persist. A message that
+        // already carries one (e.g. a kept-verbatim turn carried through
+        // compaction, or one rebuilt from disk) keeps it — only the messages
+        // freshly produced under `identity` are stamped now. This is what
+        // makes the stamp survive a later compaction onto a different model.
+        if (msg.identity == null) {
+            msg.identity = try conversation.dupeWireIdentity(alloc, identity);
+        }
+        try batch.append(alloc, .{
+            .message = msg.*,
+            .usage = msg.usage,
+            .identity = msg.identity.?,
+            .conversation = all_messages,
+            .tools_available = tools,
+        });
+    }
+
+    if (batch.items.len == 0) return;
+    try session.append(batch.items);
+}
+
+/// Persist a compaction result. The agent rewrote the conversation to
+/// `[system..., summary, kept-suffix...]`; persist everything from the
+/// latest compaction summary onward as fresh entries.
+pub fn persistCompaction(
+    alloc: Allocator,
+    session: *Session,
+    conv: *conversation.Conversation,
+    identity: WireIdentity,
+    tools: []const ToolDecl,
+) !void {
+    const start = conversation.latestCompactionIndex(conv.messages.items) orelse return;
+    try persistTurn(alloc, session, conv, start, identity, tools);
+}
+
+/// True when the assistant message at `index` contains a ToolUse block
+/// with no matching ToolResult in the immediately following user message
+/// — i.e. a dangling tool call (e.g. a turn cut short by an error).
+pub fn hasToolUseWithoutFollowingResults(
+    conv: *const conversation.Conversation,
+    index: usize,
+) bool {
+    const msg = conv.messages.items[index];
+    for (msg.content.items) |block| {
+        if (block != .ToolUse) continue;
+        if (index + 1 >= conv.messages.items.len) return true;
+        const next = conv.messages.items[index + 1];
+        if (next.role != .user) return true;
+        var found = false;
+        for (next.content.items) |next_block| {
+            if (next_block == .ToolResult and std.mem.eql(u8, next_block.ToolResult.tool_use_id, block.ToolUse.id)) {
+                found = true;
+                break;
+            }
+        }
+        if (!found) return true;
+    }
+    return false;
+}