fix: harden ensureTaskFilesCommitted merge-tree path and rename param (Sage review)

Two fixes from Sage code review of TP-163:

1. merge-tree output validation: validate the tree SHA matches a 40-hex
   OID pattern before passing it to commit-tree. git merge-tree --write-tree
   exits 0 on clean merge but could produce unexpected output in edge cases.
   An invalid SHA would cause commit-tree to fail with a confusing error.

2. executeWave param renamed baseBranch -> orchBranch: the parameter is
   always the orch branch name (batchState.orchBranch at all call sites),
   not the user's working branch. The old name caused confusion in the new
   ensureTaskFilesCommitted code that explicitly handles orch branch updates.

Workspace multi-repo gap (Sage finding #1) tracked in #479 — requires
per-repo grouping of wave tasks and is a larger change.

Author: HenryLach

extensions/taskplane/execution.ts

@@ -1536,38 +1536,48 @@ export function ensureTaskFilesCommitted(
 						repoRoot,
 					);
 					if (mergeTreeRes.ok) {
-						// First line of stdout is the merged tree SHA
+						// First line of stdout is the merged tree SHA.
+						// git merge-tree --write-tree exits 0 on clean merge, non-zero on conflicts.
+						// Since it exited 0, the tree should be conflict-free, but validate
+						// the SHA looks like a valid 40-hex OID before using it.
 						const mergedTree = mergeTreeRes.stdout.trim().split("\n")[0];
-						const mergeCommitMsg = `merge: include staged task files for wave ${waveIndex} into orch branch`;
-						const commitTreeRes = runGit(
-							["commit-tree", mergedTree, "-p", orchTip, "-p", newHead, "-m", mergeCommitMsg],
-							repoRoot,
-						);
-						if (commitTreeRes.ok) {
-							const mergeCommitSha = commitTreeRes.stdout.trim();
-							const refUpdateRes = runGit(
-								["update-ref", `refs/heads/${orchBranch}`, mergeCommitSha, orchTip],
+						if (!/^[0-9a-f]{40}$/i.test(mergedTree)) {
+							execLog("wave", `W${waveIndex}`, `warning: merge-tree returned unexpected output (non-fatal)`, {
+								orchBranch,
+								output: mergedTree.slice(0, 60),
+							});
+						} else {
+							const mergeCommitMsg = `merge: include staged task files for wave ${waveIndex} into orch branch`;
+							const commitTreeRes = runGit(
+								["commit-tree", mergedTree, "-p", orchTip, "-p", newHead, "-m", mergeCommitMsg],
 								repoRoot,
 							);
-							if (refUpdateRes.ok) {
-								execLog("wave", `W${waveIndex}`, `merged staging commit into orch branch (non-FF wave)`, {
-									orchBranch,
-									orchTip: orchTip.slice(0, 8),
-									newHead: newHead.slice(0, 8),
-									mergeCommit: mergeCommitSha.slice(0, 8),
-								});
+							if (commitTreeRes.ok) {
+								const mergeCommitSha = commitTreeRes.stdout.trim();
+								const refUpdateRes = runGit(
+									["update-ref", `refs/heads/${orchBranch}`, mergeCommitSha, orchTip],
+									repoRoot,
+								);
+								if (refUpdateRes.ok) {
+									execLog("wave", `W${waveIndex}`, `merged staging commit into orch branch (non-FF wave)`, {
+										orchBranch,
+										orchTip: orchTip.slice(0, 8),
+										newHead: newHead.slice(0, 8),
+										mergeCommit: mergeCommitSha.slice(0, 8),
+									});
+								} else {
+									execLog("wave", `W${waveIndex}`, `warning: failed to update orch branch ref after merge-tree (non-fatal)`, {
+										orchBranch,
+										error: refUpdateRes.stderr,
+									});
+								}
 							} else {
-								execLog("wave", `W${waveIndex}`, `warning: failed to update orch branch ref after merge-tree (non-fatal)`, {
+								execLog("wave", `W${waveIndex}`, `warning: failed to create merge commit for orch branch (non-fatal)`, {
 									orchBranch,
-									error: refUpdateRes.stderr,
+									error: commitTreeRes.stderr,
 								});
 							}
-						} else {
-							execLog("wave", `W${waveIndex}`, `warning: failed to create merge commit for orch branch (non-fatal)`, {
-								orchBranch,
-								error: commitTreeRes.stderr,
-							});
-						}
+						} // end valid tree SHA
 					} else {
 						execLog("wave", `W${waveIndex}`, `warning: failed to compute merge-tree for orch branch (non-fatal; requires git ≥ 2.38)`, {
 							orchBranch,
@@ -1621,7 +1631,7 @@ export function ensureTaskFilesCommitted(
  * @param batchId           - Batch ID for naming
  * @param pauseSignal       - Shared pause signal (mutated by stop-wave policy)
  * @param dependencyGraph   - Dependency graph for computing transitive dependents
- * @param baseBranch        - Branch to base worktrees on (captured at batch start)
+ * @param orchBranch        - Orch branch to base worktrees on (and to update after staging commits)
  * @param onMonitorUpdate   - Optional callback for dashboard updates during monitoring
  * @param onLanesAllocated  - Optional callback fired after lane allocation succeeds
  * @param workspaceConfig   - Workspace configuration for repo routing (null/undefined = repo mode)
@@ -1646,7 +1656,7 @@ export async function executeWave(
 	batchId: string,
 	pauseSignal: { paused: boolean },
 	dependencyGraph: DependencyGraph,
-	baseBranch: string,
+	orchBranch: string,
 	onMonitorUpdate?: MonitorUpdateCallback,
 	onLanesAllocated?: (lanes: AllocatedLane[]) => void,
 	workspaceConfig?: WorkspaceConfig | null,
@@ -1668,10 +1678,10 @@ export async function executeWave(
 	// Task folders may contain untracked files (PROMPT.md, STATUS.md) that
 	// won't appear in worktrees unless committed. Stage and commit them now,
 	// before worktree creation, so workers can find their TASK_AUTOSTART paths.
-	// Pass baseBranch (the orch branch) so the staging commit is also
-	// reflected in the orch branch before worktrees are allocated from it.
+	// Pass orchBranch so the staging commit is reflected in the orch branch
+	// before worktrees are allocated from it.
 	try {
-		ensureTaskFilesCommitted(waveTasks, pending, repoRoot, waveIndex, baseBranch);
+		ensureTaskFilesCommitted(waveTasks, pending, repoRoot, waveIndex, orchBranch);
 	} catch (err: unknown) {
 		const errMsg = err instanceof Error ? err.message : String(err);
 		execLog("wave", `W${waveIndex}`, `task file commit failed: ${errMsg}`);
@@ -1695,7 +1705,7 @@ export async function executeWave(
 	}
 
 	// ── Stage 1: Allocate lanes ──────────────────────────────────
-	const allocResult = allocateLanes(waveTasks, pending, config, repoRoot, batchId, baseBranch, workspaceConfig);
+	const allocResult = allocateLanes(waveTasks, pending, config, repoRoot, batchId, orchBranch, workspaceConfig);
 
 	if (!allocResult.success) {
 		const errMsg = allocResult.error?.message || "Unknown allocation failure";