Preserve newer trusted base config during agent restoration

actions/setup/sh/restore_base_github_folders.sh

@@ -24,6 +24,8 @@ set +o histexpand
 #                          (e.g. ".agents .claude .codex .gemini .github")
 #   GH_AW_AGENT_FILES    - space-separated list of root files to restore
 #                          (e.g. "AGENTS.md CLAUDE.md GEMINI.md")
+#   DEFAULT_BRANCH      - trusted repository default branch supplied by the
+#                          compiler for workflows with safe outputs
 #
 # Exit codes:
 #   0 - Success
@@ -38,6 +40,19 @@ SRC="/tmp/gh-aw/base"
 IFS=' ' read -ra FOLDERS <<< "${GH_AW_AGENT_FOLDERS:-}"
 IFS=' ' read -ra ROOT_FILES <<< "${GH_AW_AGENT_FILES:-}"
 
+# A trusted base checkout may have advanced since activation. Replacing its config
+# with the old snapshot would turn concurrent base changes into agent-authored
+# reverts. Only an exact commit match is sufficient; a PR head can also descend
+# from the base. Missing refs (including checkout-disabled runs) retain restoration.
+if [ -n "${DEFAULT_BRANCH:-}" ] &&
+  HEAD_SHA=$(git -C "${WORKSPACE}" rev-parse --verify 'HEAD^{commit}' 2>/dev/null) &&
+  BASE_SHA=$(git -C "${WORKSPACE}" rev-parse --verify "refs/remotes/origin/${DEFAULT_BRANCH}^{commit}" 2>/dev/null) &&
+  [ "${HEAD_SHA}" = "${BASE_SHA}" ]; then
+  echo "Keeping agent config folders from the checked-out trusted base commit ${HEAD_SHA}"
+  FOLDERS=()
+  ROOT_FILES=()
+fi
+
 for FOLDER in "${FOLDERS[@]+"${FOLDERS[@]}"}"; do
   SNAPSHOT="${SRC}/${FOLDER}"
   DEST="${WORKSPACE}/${FOLDER}"

docs/src/content/docs/engines/copilot.md

@@ -64,7 +64,7 @@ engine:
 
 gh-aw enables the CLI's `EXTENSIONS` feature flag, loads project extensions in prompt mode, and pre-approves workflow runs. SDK sessions honor the same switch through their tool catalog and permission handler, without granting additional shell or MCP access. Save reusable definitions and supporting files under `.github/extensions/<name>/extension.mjs`, and explicitly request the registered workflow by name in the prompt. Their agents remain subject to the configured tool permissions and sandbox policies.
 
-gh-aw's existing engine-config restoration snapshots the engine-declared folders, including Copilot's `.github/`, recursively from the activation checkout and restores them after agent checkouts, including when `checkout.pull-request: false` is set. Restoring the entire configuration directory prevents PR-head extension code, settings, and hooks from replacing trusted definitions. Use `ambient-folders` for supporting files elsewhere in the repository. Dynamic workflow availability also depends on the Copilot account; enabling extensions does not make workflows available with a BYOK provider.
+gh-aw's existing engine-config restoration snapshots the engine-declared folders, including Copilot's `.github/`, recursively from the activation checkout and restores them after agent checkouts, including when `checkout.pull-request: false` is set. For workflows with safe outputs, a checkout whose HEAD exactly matches the local default-branch remote-tracking ref keeps its current configuration instead, preserving base-branch updates that landed after activation. PR heads that merely descend from the base still receive snapshot restoration. Restoring the entire configuration directory prevents PR-head extension code, settings, and hooks from replacing trusted definitions. Use `ambient-folders` for supporting files elsewhere in the repository. Dynamic workflow availability also depends on the Copilot account; enabling extensions does not make workflows available with a BYOK provider.
 
 The repository's [Copilot dynamic workflow smoke test](https://github.com/github/gh-aw/blob/main/.github/workflows/smoke-copilot-dynamic-workflow.md) invokes the packaged `smoke-copilot-dynamic-workflow` extension by name. It verifies a relative module import, a nested hidden support file, durable steps, and one structured subagent result. Run it with `gh aw run smoke-copilot-dynamic-workflow`, or dispatch **Smoke Trigger** with `dynamic-workflow: true` to exercise a feature branch before the new workflow is registered on the default branch.
 

docs/src/content/docs/reference/safe-outputs-pull-requests.md

@@ -149,6 +149,8 @@ The agent's commits are packaged as a **git bundle** and uploaded as an Actions
 
 If the base branch advances between agent start and `safe_outputs` apply, the PR is created slightly behind the current base — normal behavior the author can address with a rebase. If a non-fast-forward race occurs during the push itself, the job creates a fallback PR from a temporary branch so no changes are lost.
 
+If the default branch advances between activation and the agent checkout, configuration restoration keeps the newer checkout's config folders and root instruction files when HEAD exactly matches its local default-branch remote-tracking ref. It does not overwrite them with the older activation snapshot. PR or feature-branch checkouts and checkouts without that local ref retain snapshot restoration; no additional fetch is required.
+
 An older **patch transport** (`git format-patch` / `git am --3way`) is used when bundle data is unavailable. `--3way` resolves cleanly against an updated base when there are no conflicts; if it cannot, the patch is applied at the agent's original base commit and the PR UI shows the conflicts for manual resolution.
 
 :::caution[Shallow checkout and large monorepos]

pkg/workflow/pr_test.go

@@ -425,6 +425,104 @@ func TestCanRestoreAgentConfigFolders(t *testing.T) {
 	}
 }
 
+func TestRestoreConfigWhenBaseAdvances(t *testing.T) {
+	restoreScript, err := os.ReadFile(filepath.Join("..", "..", "actions", "setup", "sh", "restore_base_github_folders.sh"))
+	require.NoError(t, err)
+	for _, mode := range []string{"trusted base", "PR head", "missing base ref", "missing default branch input"} {
+		t.Run(mode, func(t *testing.T) {
+			root := t.TempDir()
+			workspace := filepath.Join(root, "workspace")
+			base := filepath.Join(root, "base")
+			require.NoError(t, os.MkdirAll(workspace, 0755))
+			git := func(args ...string) string {
+				t.Helper()
+				cmd := exec.Command("git", args...)
+				cmd.Dir = workspace
+				cmd.Env = append(os.Environ(), "GIT_CONFIG_NOSYSTEM=1", "GIT_CONFIG_GLOBAL=/dev/null")
+				output, err := cmd.CombinedOutput()
+				require.NoError(t, err, string(output))
+				return strings.TrimSpace(string(output))
+			}
+			write := func(name, content string) {
+				t.Helper()
+				dest := filepath.Join(workspace, name)
+				require.NoError(t, os.MkdirAll(filepath.Dir(dest), 0755))
+				require.NoError(t, os.WriteFile(dest, []byte(content), 0644))
+			}
+			git("init", "-q")
+			git("config", "user.name", "Test")
+			git("config", "user.email", "test@example.com")
+			git("config", "commit.gpgsign", "false")
+			write(".github/workflows/publish.yml", "original workflow\n")
+			write(".claude/removed.md", "original config\n")
+			write("AGENTS.md", "original instructions\n")
+			write("result.txt", "before\n")
+			git("add", ".")
+			git("commit", "-qm", "Activation base A")
+			require.NoError(t, os.MkdirAll(filepath.Join(base, ".github", "workflows"), 0755))
+			require.NoError(t, os.MkdirAll(filepath.Join(base, ".claude"), 0755))
+			require.NoError(t, os.WriteFile(filepath.Join(base, ".github", "workflows", "publish.yml"), []byte("original workflow\n"), 0644))
+			require.NoError(t, os.WriteFile(filepath.Join(base, ".claude", "removed.md"), []byte("original config\n"), 0644))
+			require.NoError(t, os.WriteFile(filepath.Join(base, "AGENTS.md"), []byte("original instructions\n"), 0644))
+
+			write(".github/workflows/publish.yml", "original workflow\nconcurrent base step\n")
+			write(".claude/new.md", "concurrent config\n")
+			require.NoError(t, os.Remove(filepath.Join(workspace, ".claude", "removed.md")))
+			require.NoError(t, os.Remove(filepath.Join(workspace, "AGENTS.md")))
+			git("add", "-A")
+			git("commit", "-qm", "Concurrent base B")
+			baseSHA := git("rev-parse", "HEAD")
+			defaultBranch := "main"
+			if mode != "missing base ref" {
+				git("update-ref", "refs/remotes/origin/"+defaultBranch, baseSHA)
+			}
+			if mode == "PR head" {
+				// An ancestor match would incorrectly trust this PR's config.
+				git("checkout", "-qb", "untrusted-pr")
+				write(".github/workflows/publish.yml", "untrusted workflow\n")
+				write(".claude/injected.md", "untrusted config\n")
+				write("AGENTS.md", "untrusted instructions\n")
+				git("add", "-A")
+				git("commit", "-qm", "Untrusted PR")
+			}
+			write(".mcp.json", `{"mcpServers":{"untrusted":{}}}`)
+			scriptPath := filepath.Join(root, "restore.sh")
+			isolatedScript := strings.ReplaceAll(string(restoreScript), `SRC="/tmp/gh-aw/base"`, "SRC="+shellEscapeArg(base))
+			require.NoError(t, os.WriteFile(scriptPath, []byte(isolatedScript), 0644))
+			if mode == "missing default branch input" {
+				defaultBranch = ""
+			}
+			cmd := exec.Command("bash", scriptPath)
+			cmd.Env = append(os.Environ(),
+				"GITHUB_WORKSPACE="+workspace,
+				"GH_AW_AGENT_FOLDERS=.github .claude",
+				"GH_AW_AGENT_FILES=AGENTS.md",
+				"DEFAULT_BRANCH="+defaultBranch,
+			)
+			output, err := cmd.CombinedOutput()
+			require.NoError(t, err, string(output))
+			assert.NoFileExists(t, filepath.Join(workspace, ".mcp.json"))
+			if mode == "trusted base" {
+				assert.Contains(t, string(output), "checked-out trusted base commit")
+				assert.Empty(t, git("status", "--porcelain"))
+				write("result.txt", "agent result\n")
+				git("add", "-A")
+				git("commit", "-qm", "Agent change")
+				assert.Equal(t, baseSHA, git("rev-parse", "HEAD^"))
+				assert.Equal(t, "result.txt", git("diff", "--name-only", baseSHA, "HEAD"))
+			} else {
+				content, err := os.ReadFile(filepath.Join(workspace, ".github", "workflows", "publish.yml"))
+				require.NoError(t, err)
+				assert.Equal(t, "original workflow\n", string(content))
+				assert.FileExists(t, filepath.Join(workspace, ".claude", "removed.md"))
+				assert.NoFileExists(t, filepath.Join(workspace, ".claude", "new.md"))
+				assert.NoFileExists(t, filepath.Join(workspace, ".claude", "injected.md"))
+				assert.FileExists(t, filepath.Join(workspace, "AGENTS.md"))
+			}
+		})
+	}
+}
+
 func TestEngineConfigRestorePrecedesAgentSteps(t *testing.T) {
 	enabled, disabled := true, false
 	for _, engineID := range []string{"claude", "copilot"} {