Use session working directory in loc-breakdown canvas (#17862)

* Use session working directory in loc-breakdown canvas

Forked extension processes inherit a cwd of ~/.copilot, which is not a
git repo. With no explicit cwd input, buildReport ran git commands there
and /data returned HTTP 500, surfacing as a load error in the canvas UI.

Prefer the runtime-supplied ctx.session.workingDirectory (the user's
worktree/repo) over process.cwd() in both the open handler and the
refresh action's fallback path.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Address review nits on cwd fallback wording

- Update inputSchema cwd description to reflect that the session
  working directory is the primary default, with process.cwd() as
  a last-resort fallback.
- Soften the inline comment on the open handler: the issue is that
  the extension process cwd is not necessarily the target session
  repo, not that ~/.copilot is never a git repo.
- Mirror the docs update in the README's optional-inputs section.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

---------

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: mitchdenny

.github/extensions/loc-breakdown/README.md

@@ -40,7 +40,7 @@ action the agent can invoke to recompute the report.
 
 Optional inputs when opening the canvas:
 
-- `cwd` — working directory inside a git repo (defaults to the agent's cwd)
+- `cwd` — working directory inside a git repo (defaults to the active session's working directory, falling back to the extension process cwd)
 - `base` — base ref to diff against (defaults to `origin/HEAD`)
 - `head` — head ref (defaults to `HEAD`)
 

.github/extensions/loc-breakdown/extension.mjs

@@ -483,7 +483,7 @@ await joinSession({
             inputSchema: {
                 type: "object",
                 properties: {
-                    cwd: { type: "string", description: "Working directory inside the target git repo. Defaults to the canvas process cwd." },
+                    cwd: { type: "string", description: "Working directory inside the target git repo. Defaults to the active session's working directory (the user's worktree/repo); falls back to the extension process cwd only if the runtime did not supply one." },
                     base: { type: "string", description: "Base ref to diff against. Defaults to origin/HEAD." },
                     head: { type: "string", description: "Head ref. Defaults to HEAD." },
                 },
@@ -494,7 +494,9 @@ await joinSession({
                     description: "Recompute the LOC breakdown by re-running git diff and return the latest report as JSON.",
                     handler: async (ctx) => {
                         const entry = servers.get(ctx.instanceId);
-                        const opts = entry ? entry.opts : { cwd: process.cwd() };
+                        // Fall back to the session working directory (the user's worktree/repo) before
+                        // process.cwd(), which for forked extensions is typically ~/.copilot and not a git repo.
+                        const opts = entry ? entry.opts : { cwd: ctx.session?.workingDirectory || process.cwd() };
                         const report = await buildReport(opts);
                         return {
                             ok: true,
@@ -513,8 +515,13 @@ await joinSession({
             ],
             open: async (ctx) => {
                 const input = ctx.input || {};
+                // Prefer the explicit input.cwd, then the session's working directory supplied by
+                // the runtime (CanvasSessionContext.workingDirectory). process.cwd() is a last resort
+                // because the extension process cwd is not necessarily the target session's repo —
+                // for forked extensions it's typically ~/.copilot, which is the wrong repo for this
+                // report even on the rare setups where it happens to be a git repo itself.
                 const opts = {
-                    cwd: input.cwd || process.cwd(),
+                    cwd: input.cwd || ctx.session?.workingDirectory || process.cwd(),
                     base: input.base,
                     head: input.head,
                 };