diff --git a/README.md b/README.md
index c914266b..3c650c00 100644
--- a/README.md
+++ b/README.md
@@ -60,7 +60,7 @@ npm run service:backup-check -- --input "/absolute/private/outside-repo/tinystud
 
 The export takes the shared service lock and rejects pending promotions, symlinks, special files, in-repo or existing destinations, unsafe permissions, and changed bytes. Restore only into a clean clone: verify the snapshot; copy `clients/`, `prospects/`, `service-decisions/`, and `runs/service-engine/outputs/` to the same relative paths without merging or overwriting; run `npm run service:queue -- --mode=prepare --scope all`; then run `npm run service:queue-check -- --scope all`. Keep the snapshot local until a human approves its storage destination, access, retention, and deletion policy.
 
-The Friday retention-prep automation is optional only while there are no client records. Once a client exists, `retention:automation-check` fails closed and prints the exact replacement prompt. Independently of client records, the check refuses to pass on a checkout that is behind remote main (remote `refs/heads/main` must be an ancestor of the local HEAD, proven by bounded `ls-remote`/`fetch`) or on an isolated empty checkout whose canonical state roots (`clients/`, `prospects/`) do not exist as real directories in the repository's main worktree.
+The Friday retention-prep automation is optional only while there are no client records. Once a client exists, `retention:automation-check` fails closed and prints the exact replacement prompt. Independently of client records, the check refuses to pass on a checkout that is behind remote main (remote `refs/heads/main` must be an ancestor of the local HEAD, proven by bounded `ls-remote`/`fetch`), on a canonical retention workspace that is itself behind remote main (the Friday loop would run its old gate code), or on an isolated empty checkout whose canonical state roots (`clients/`, `prospects/`) do not exist as real directories in the repository's main worktree. The canonical workspace is the git main worktree — the first entry of `git worktree list`, which owns the repository's `.git` — never a twin worktree that merely happens to hold the `refs/heads/main` branch while the main worktree is detached.
 
 Run the checks before treating a packet as ready:
 
diff --git a/scripts/check-retention-automation.mjs b/scripts/check-retention-automation.mjs
index 88076da6..f54472d3 100644
--- a/scripts/check-retention-automation.mjs
+++ b/scripts/check-retention-automation.mjs
@@ -4,7 +4,7 @@ import {dirname, join} from "node:path";
 import {homedir} from "node:os";
 import {fileURLToPath} from "node:url";
 import {RETENTION_AUTOMATION_PROMPT} from "./lib/retention-automation.mjs";
-import {canonicalMainWorktree, normalizedPath, runPreflight, scriptRepoRoot} from "./lib/retention-preflight.mjs";
+import {canonicalMainWorktree, normalizedPath, proveFreshness, runPreflight, scriptRepoRoot} from "./lib/retention-preflight.mjs";
 
 const automationId = "tinystudio-retention-checkups";
 const codexHome = process.env.CODEX_HOME || join(homedir(), ".codex");
@@ -18,6 +18,17 @@ const clientCount = preflight.activeClients;
 const failures = [...preflight.failures];
 const warnings = [...preflight.warnings];
 
+// The Friday loop runs from the canonical retention workspace, so that
+// workspace itself must not be a stale checkout running old gate code. When
+// the script runs from the same checkout the preflight already proved it;
+// otherwise prove the canonical workspace directly.
+const expectedRepo = normalizedPath(expectedCwd);
+const canonicalFreshness =
+  normalizedPath(repoForFreshness) === expectedRepo ? preflight.freshness : proveFreshness(expectedCwd);
+if (canonicalFreshness && canonicalFreshness.ok === false) {
+  failures.push(`retention workspace is stale: ${canonicalFreshness.reason}`);
+}
+
 function value(content, key) {
   const match = String(content || "").match(new RegExp(`^${key}\\s*=\\s*"([^"]*)"`, "m"));
   return match ? match[1] : "";
@@ -84,7 +95,6 @@ const cadence = value(content, "rrule");
 if (value(content, "id") !== automationId) failures.push("Automation id does not match TinyStudio retention checkups");
 if (value(content, "kind") !== "cron") failures.push("Automation is not a cron automation");
 if (value(content, "status") !== "ACTIVE") failures.push("Automation is not active");
-const expectedRepo = normalizedPath(expectedCwd);
 const configuredRepos = configuredWorkspacePaths(content).map(normalizedPath);
 if (!configuredRepos.includes(expectedRepo)) failures.push("Automation does not point at the TinyStudio repo");
 if (!/^FREQ=WEEKLY;/.test(cadence) || !cadence.includes("BYDAY=FR")) failures.push("Automation is not scheduled as the weekly Friday retention loop");
diff --git a/scripts/lib/retention-preflight.mjs b/scripts/lib/retention-preflight.mjs
index 69956985..7f01feea 100644
--- a/scripts/lib/retention-preflight.mjs
+++ b/scripts/lib/retention-preflight.mjs
@@ -64,6 +64,12 @@ export function normalizedPath(path) {
 	}
 }
 
+// Resolves the repository's main worktree: the entry that owns the repository's
+// .git directory, which `git worktree list` always reports first. Hosting the
+// `refs/heads/main` branch is not the same as being the main worktree — a
+// detached main worktree leaves `main` checked out in some other worktree, and
+// substituting that twin here would turn the canonical-state inspection into a
+// hollow pass on the twin's (possibly stale, empty) state root.
 export function canonicalMainWorktree(repoRoot) {
 	try {
 		const output = execFileSync("git", ["-C", repoRoot, "worktree", "list", "--porcelain"], {
@@ -71,10 +77,8 @@ export function canonicalMainWorktree(repoRoot) {
 			stdio: ["ignore", "pipe", "ignore"],
 			timeout: GIT_TIMEOUT_MS
 		})
-		let worktree = ""
 		for (const line of output.split("\n")) {
-			if (line.startsWith("worktree ")) worktree = line.slice("worktree ".length)
-			if (line === "branch refs/heads/main" && worktree) return worktree
+			if (line.startsWith("worktree ")) return line.slice("worktree ".length)
 		}
 	} catch {}
 	return repoRoot
diff --git a/scripts/test-retention-automation.mjs b/scripts/test-retention-automation.mjs
index 14015e39..5dd81ce8 100644
--- a/scripts/test-retention-automation.mjs
+++ b/scripts/test-retention-automation.mjs
@@ -37,8 +37,8 @@ function writeAutomationSingular(prompt, workspace = repoDir) {
 	writeFileSync(automationPath, `id = "tinystudio-retention-checkups"\nkind = "cron"\nname = "TinyStudio retention checkups"\nprompt = "${prompt}"\nstatus = "ACTIVE"\nrrule = "FREQ=WEEKLY;BYDAY=FR;BYHOUR=9;BYMINUTE=0"\nworkspace = "${workspace}"\n`)
 }
 
-function run(github = "false") {
-	return spawnSync(process.execPath, [script], {cwd: fixtureRoot, env: {...process.env, CODEX_HOME: codexHome, GITHUB_ACTIONS: github, SERVICE_REPO_ROOT: serviceRoot, TINYSTUDIO_PREFLIGHT_REPO: repoDir}, encoding: "utf8"})
+function run(github = "false", preflightRepo = repoDir) {
+	return spawnSync(process.execPath, [script], {cwd: fixtureRoot, env: {...process.env, CODEX_HOME: codexHome, GITHUB_ACTIONS: github, SERVICE_REPO_ROOT: serviceRoot, TINYSTUDIO_PREFLIGHT_REPO: preflightRepo}, encoding: "utf8"})
 }
 
 try {
@@ -222,6 +222,42 @@ try {
 	eq(result.status, 0)
 	eq(JSON.parse(result.stdout).status, "pass")
 
+	// Closed-twin regression: when the repository's main worktree is detached,
+	// `refs/heads/main` gets checked out in some other worktree (the twin). The
+	// twin must never become the canonical retention workspace: the gate has to
+	// keep inspecting the main worktree's state, and the automation still has
+	// to point at the main worktree, not the twin.
+	const twinDir = join(fixtureRoot, "twin")
+	runGit(repoDir, ["checkout", "--detach"])
+	runGit(repoDir, ["worktree", "add", twinDir, "main"])
+
+	// Automation pointed at the main worktree still passes while the twin holds
+	// the main branch.
+	writeAutomation(RETENTION_AUTOMATION_PROMPT, repoDir)
+	result = run()
+	eq(result.status, 0)
+	eq(JSON.parse(result.stdout).status, "pass")
+
+	// Automation pointed at the twin fails: the twin is not the TinyStudio repo.
+	writeAutomation(RETENTION_AUTOMATION_PROMPT, twinDir)
+	result = run()
+	neq(result.status, 0)
+	out = JSON.parse(result.stdout)
+	assert(out.failures.includes("Automation does not point at the TinyStudio repo"), "twin workspace must not be accepted as the TinyStudio repo")
+
+	// A stale canonical workspace fails even when the gate runs from a fresh
+	// checkout elsewhere in the same repository: the Friday loop would run the
+	// canonical workspace's old gate code.
+	const staleBase = runGit(repoDir, ["rev-parse", "HEAD~1"])
+	runGit(repoDir, ["reset", "--hard", staleBase])
+	writeAutomation(RETENTION_AUTOMATION_PROMPT, repoDir)
+	result = run("false", twinDir)
+	neq(result.status, 0)
+	out = JSON.parse(result.stdout)
+	assert(out.failures.includes("retention workspace is stale: checkout is behind or diverged from remote main"), "stale canonical workspace must fail closed even when the gate runs from a fresh checkout")
+	assert(!out.failures.includes("Automation does not point at the TinyStudio repo"), "stale canonical workspace must fail on staleness, not on the workspace pointer")
+	runGit(repoDir, ["reset", "--hard", remoteSha])
+
 	console.log("Retention automation applicability checks passed.")
 } finally {
 	rmSync(fixtureRoot, {recursive: true, force: true})