1 files changed, 48 insertions, 3 deletions

diff --git a/build.zig b/build.zig
index bcfe1be..659638a 100644
--- a/build.zig
+++ b/build.zig
@@ -316,9 +316,18 @@ fn generateLuarocksEmbed(
 /// `$PANTO_HOME/agent/` on first run, where the runtime's extension
 /// loader finds it as the "system" layer (below user and project).
 ///
-/// Mirrors `generateLuarocksEmbed`'s addCopyDirectory trick so the
-/// emitted `@embedFile("agent_src/<rel>")` references resolve relative
-/// to the generated zig file.
+/// Unlike `generateLuarocksEmbed`, the agent tree lives in-repo and
+/// its contents change as we add/edit tools. `addDirectoryArg` on a
+/// local source dir does NOT hash directory contents into the cache
+/// key (only the path string), so editing a file under `agent/`
+/// wouldn't invalidate this step's cache. To make cache invalidation
+/// correct, we enumerate the tree at *build-script execution time*
+/// and call `addFileInput` for every file we find. Each file then
+/// participates in the cache key.
+///
+/// `addCopyDirectory` (below) still does the actual staging of the
+/// tree alongside the generated zig file so `@embedFile("agent_src/...")`
+/// references resolve.
 fn generateAgentEmbed(b: *std.Build) std.Build.LazyPath {
     const tool = b.addExecutable(.{
         .name = "gen-agent-embed",
@@ -336,12 +345,48 @@ fn generateAgentEmbed(b: *std.Build) std.Build.LazyPath {
     run.addDirectoryArg(b.path("agent"));
     const gen_file = run.addOutputFileArg("embedded_agent.zig");
 
+    // Enumerate every file under `agent/` and register it as an
+    // explicit cache input. This is what makes `zig build` notice
+    // edits to e.g. `agent/tools/read.lua` without a manual
+    // `rm -rf .zig-cache`.
+    addAgentTreeFileInputs(b, run, "agent") catch |err| {
+        std.debug.panic("failed to enumerate agent/ tree: {t}", .{err});
+    };
+
     const wf = b.addWriteFiles();
     const out_zig = wf.addCopyFile(gen_file, "embedded_agent.zig");
     _ = wf.addCopyDirectory(b.path("agent"), "agent_src", .{});
     return out_zig;
 }
 
+/// Recursively walk `subpath` under the build root and call
+/// `addFileInput` on every regular file. Used to give the agent-embed
+/// codegen accurate cache invalidation. Dotfiles (any path segment
+/// starting with `.`) are skipped to match the codegen's filter.
+fn addAgentTreeFileInputs(
+    b: *std.Build,
+    run: *std.Build.Step.Run,
+    subpath: []const u8,
+) !void {
+    const io = b.graph.io;
+    var dir = b.build_root.handle.openDir(io, subpath, .{ .iterate = true }) catch |err| switch (err) {
+        error.FileNotFound => return,
+        else => return err,
+    };
+    defer dir.close(io);
+
+    var walker = try dir.walk(b.allocator);
+    defer walker.deinit();
+
+    while (try walker.next(io)) |entry| {
+        if (entry.kind != .file) continue;
+        if (entry.basename.len == 0 or entry.basename[0] == '.') continue;
+        if (std.mem.indexOf(u8, entry.path, "/.") != null) continue;
+        const rel = b.pathJoin(&.{ subpath, entry.path });
+        run.addFileInput(b.path(rel));
+    }
+}
+
 /// Codegen step: emit a Zig module that exposes every Lua public header
 /// from the Lua source tarball as embedded bytes. The bootstrap stages
 /// these under `$PANTO_HOME/rocks/lua-X.Y.Z/include/` so luarocks can