test(gate): witness A6 in both consumers; bound the negative path

Three findings, all upheld.

1. A6 was witnessed only for the helper. Both consumers now have real
   -path rows.

   Gate side, driven through a stub worktree --- a temp git repo holding
   a copy of scripts/gate and a controlled helper --- so the gate's own
   code path runs against each verdict without touching the checked-in
   helper: a stub exiting 2 refuses with the ERROR wording and never
   "SIGINT is ignored"; a NON-EXECUTABLE stub maps 126 to boundary
   error 2 with its own wording. That second case is what the original
   guard got wrong twice.

   R-d side: the precondition is split into sigint_diagnosis() ->
   Result, so the message is testable rather than reachable only
   through a panic in a test that cannot run under the condition it
   describes. The new row asserts safe proceeds, ignored says so and
   says "NOT a teardown defect", error says "could not determine" and
   never "ignored", and an unrunnable helper is undecidable at the
   boundary.

2. The refusal row violated this suite's no-recursion constraint: it
   invoked the ordinary gate, so a regression of the exact `if !` bug
   would have launched eight real gate stages inside the gate suite.
   It now uses --self-test, which drives the same runner over a
   hardcoded synthetic plan, so the negative path stays bounded
   whatever the guard does. under_ignored_sigint() also takes the
   program and arguments POSITIONALLY --- `exec "$@"` --- instead of
   interpolating them into script text, which broke for any path
   containing a space or shell metacharacter, and every path here comes
   from a tempdir or CARGO_MANIFEST_DIR.

3. The portable checkpoint is recorded: implementation at 3206433,
   pushed, signed, clean, full default gate green 8/8 foreground. The
   framing header no longer says implementation "may proceed" --- it
   reports IMPLEMENTED. And docs/agent-handoff.md §3 gains the durable
   rule: never start the gate or cargo test from a shell that ignores
   SIGINT, `setsid nohup ... &` is forbidden, SIG_IGN is inherited
   across fork and survives exec, the gate refuses with no override,
   and scripts/check-sigint-deliverable answers the question directly.

35 gate-acceptance rows, 16 gpu_invocation_acceptance rows, full gate
green.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016bqGA6s9tTUFzYpbeW3tai

docs/active-work.md

@@ -279,6 +279,15 @@ from #171 and #215.
   **`72da24a`**, worktree
   `/home/jeans/Repos/personal/pmacs-probe-sigint`. Recover with
   `git fetch githubsucks && git checkout gpu-probe-sigint-teardown`.
+- **CHECKPOINT: implementation landed at `3206433`; this entry's own
+  commit adds the A6 consumer rows on top.** The branch head is the
+  authority — a literal SHA naming a branch's own tip goes stale the
+  moment the next commit lands, which this ledger has already recorded
+  once. State at `3206433`: pushed, signed `G`, worktree clean,
+  `git diff --check` clean, **full default gate green (8/8) in the
+  foreground**, 31 gate-acceptance rows passing. After this commit:
+  **35 gate-acceptance rows and 16 `gpu_invocation_acceptance` rows**,
+  with the full gate re-run.
 - **No PR. Framing revision 12 at `docs/gpu-probe-sigint-framing.md`,
   APPROVED 2026-08-19 at `1fc0df6`** — revision 10 was approved at
   `4fba9f6` and revision 9 at `15c25ec`; neither approval covered the

docs/agent-handoff.md

@@ -2547,6 +2547,34 @@ its own step, never `&&`-chained.
 
 **Run it with `scripts/gate`. Do not retype it.**
 
+**NEVER start the gate — or `cargo test` — from a shell that ignores
+`SIGINT`.** A shell backgrounding a job without job control sets
+`SIGINT` (and `SIGQUIT`) to `SIG_IGN`; `nohup` adds `SIGHUP`. `SIG_IGN`
+is **inherited across `fork` and survives `exec`**, so it reaches
+`cargo`, the test binary, and everything they spawn. Any test that
+signals a child and waits for it then hangs to its own deadline and
+reports a *product* defect that is not there.
+
+Concretely: `setsid nohup ./scripts/gate … &` is **forbidden**. This
+cost one lane seven red full sweeps and nine framing revisions chasing
+a GPU teardown bug that never existed
+(`docs/gpu-probe-sigint-framing.md` §4c). Long runs do not need it —
+measured, an ordinary tool-level background launch leaves `SIGINT`
+deliverable.
+
+`scripts/gate` now refuses to start in that state, before any stage,
+and **there is no override**: a run under ignored `SIGINT` cannot
+produce valid evidence. If you see
+
+```
+pmacs: SIGINT is ignored; run this command with SIGINT deliverable
+gate: REFUSING TO RUN --- see the diagnosis above.
+```
+
+the fix is to re-run it in the foreground, not to work around the
+guard. `scripts/check-sigint-deliverable` answers the question on its
+own: exit **0** deliverable, **1** ignored, **2** undecidable.
+
 ```
 scripts/gate [--acceptance SUITE]... [--protocol]
 ```

docs/gpu-probe-sigint-framing.md

@@ -1,8 +1,8 @@
 # GPU launcher / probe SIGINT teardown — framing
 
-Revision 12. Status: **APPROVED 2026-08-19 at `1fc0df6`.
-MECHANISM FOUND (§4c), REMEDY SELECTED (§7c); implementation may
-proceed under §8's A1–A7 contract.**
+Revision 12, approved 2026-08-19 at `7752bcb`.
+Status: **IMPLEMENTED — R-b + R-d landed and witnessed (§8). Mechanism
+in §4c; no product change.**
 
 Revision 10 was approved 2026-08-19 at `4fba9f6`, authorising
 diagnostic-only D1/D2. They ran, and found the mechanism on the first

tests/gate_script_acceptance.rs

@@ -48,12 +48,57 @@ fn sigint_helper() -> PathBuf {
 /// inherited across `fork` **and survives `exec`** — which is the whole
 /// mechanism under test, so simulating it this way exercises the real
 /// thing rather than a stand-in.
-fn under_ignored_sigint(cmd: &str) -> std::process::Output {
-    Command::new("sh")
+fn under_ignored_sigint(
+    program: &Path,
+    args: &[&str],
+    cwd: &Path,
+    env: &[(&str, &str)],
+) -> std::process::Output {
+    // `exec "$@"` with the program and arguments passed POSITIONALLY.
+    // Interpolating them into the script text would break on any path
+    // containing a space or a shell metacharacter, and every path here
+    // comes from a `tempdir` or `CARGO_MANIFEST_DIR` — neither of which
+    // this test controls.
+    let mut command = Command::new("sh");
+    command
         .arg("-c")
-        .arg(format!("trap \"\" INT; {cmd}"))
-        .output()
-        .expect("spawn shell with SIGINT ignored")
+        .arg("trap \"\" INT; exec \"$@\"")
+        .arg("sh")
+        .arg(program)
+        .args(args)
+        .current_dir(cwd);
+    for (key, value) in env {
+        command.env(key, value);
+    }
+    command.output().expect("spawn shell with SIGINT ignored")
+}
+
+/// A minimal git worktree holding a copy of `scripts/gate` and a
+/// **stub** `check-sigint-deliverable`, so the gate's handling of each
+/// helper status can be driven on its real path without touching the
+/// checked-in helper.
+fn gate_with_stub_helper(stub_body: &str, executable: bool) -> tempfile::TempDir {
+    let dir = tempfile::tempdir().expect("tempdir");
+    let scripts = dir.path().join("scripts");
+    std::fs::create_dir_all(&scripts).expect("scripts dir");
+    std::fs::copy(gate(), scripts.join("gate")).expect("copy gate");
+    let helper = scripts.join("check-sigint-deliverable");
+    std::fs::write(&helper, stub_body).expect("write stub helper");
+    let mode = if executable { 0o755 } else { 0o644 };
+    std::fs::set_permissions(&helper, std::os::unix::fs::PermissionsExt::from_mode(mode))
+        .expect("chmod stub helper");
+    std::fs::set_permissions(
+        scripts.join("gate"),
+        std::os::unix::fs::PermissionsExt::from_mode(0o755),
+    )
+    .expect("chmod gate copy");
+    let ok = Command::new("git")
+        .args(["init", "-q"])
+        .current_dir(dir.path())
+        .status()
+        .expect("git init");
+    assert!(ok.success(), "the stub worktree must be a git worktree");
+    dir
 }
 
 fn gate() -> PathBuf {
@@ -114,6 +159,68 @@ fn run(root: &Path, args: &[&str]) -> (String, String, bool) {
 // §3, nothing else in the repository would notice. `--print-plan`
 // exists to make that checkable without executing anything.
 
+/// A6, gate consumer: a helper verdict of `error` (2) refuses the run
+/// with the ERROR wording, and never claims `SIGINT` is ignored.
+///
+/// Driven through a stub worktree so the gate's real code path runs
+/// against a controlled helper status; the helper's own classification
+/// is covered by its own rows above.
+#[test]
+fn gate_refuses_on_helper_error_without_claiming_sigint_is_ignored() {
+    let root = tempfile::tempdir().expect("tempdir");
+    let repo = gate_with_stub_helper(
+        "#!/bin/sh\necho 'pmacs: could not determine whether SIGINT is deliverable (probe status 42)' >&2\nexit 2\n",
+        true,
+    );
+    let out = Command::new(repo.path().join("scripts/gate"))
+        .arg("--self-test")
+        .current_dir(repo.path())
+        .env("PMACS_GATE_TARGET_ROOT", root.path())
+        .output()
+        .expect("run the stub-worktree gate");
+    assert_eq!(
+        out.status.code(),
+        Some(2),
+        "an error verdict exits 2, not 1"
+    );
+    let err = String::from_utf8_lossy(&out.stderr);
+    assert!(err.contains("could not determine"), "error wording: {err}");
+    assert!(
+        !err.contains("SIGINT is ignored"),
+        "an undecidable probe must never be reported as ignored: {err}"
+    );
+    assert!(err.contains("no stage has run"), "and no stage ran: {err}");
+}
+
+/// A6, gate boundary: a helper that cannot be EXECUTED is an `error` at
+/// the call boundary — mapped to 2 — never evidence that `SIGINT` is
+/// ignored.
+///
+/// This is the case the original guard got wrong twice: under `set -e`
+/// a bare invocation died before any mapping, and 126/127 would have
+/// escaped raw.
+#[test]
+fn gate_maps_an_unexecutable_helper_to_error_not_ignored() {
+    let root = tempfile::tempdir().expect("tempdir");
+    let repo = gate_with_stub_helper("#!/bin/sh\nexit 0\n", false);
+    let out = Command::new(repo.path().join("scripts/gate"))
+        .arg("--self-test")
+        .current_dir(repo.path())
+        .env("PMACS_GATE_TARGET_ROOT", root.path())
+        .output()
+        .expect("run the stub-worktree gate");
+    assert_eq!(out.status.code(), Some(2), "boundary failures map to 2");
+    let err = String::from_utf8_lossy(&out.stderr);
+    assert!(
+        err.contains("could not run the SIGINT guard"),
+        "the boundary has its own wording: {err}"
+    );
+    assert!(
+        !err.contains("SIGINT is ignored"),
+        "an unrunnable guard is not evidence about the signal: {err}"
+    );
+}
+
 /// §7c: the helper answers `safe` when `SIGINT` is deliverable.
 #[test]
 fn sigint_helper_reports_safe_when_the_signal_is_deliverable() {
@@ -132,7 +239,7 @@ fn sigint_helper_reports_safe_when_the_signal_is_deliverable() {
 /// `SIGINT` is inherited as `SIG_IGN`.
 #[test]
 fn sigint_helper_reports_ignored_when_the_signal_is_inherited_ignored() {
-    let out = under_ignored_sigint(&format!("{}", sigint_helper().display()));
+    let out = under_ignored_sigint(&sigint_helper(), &[], &repo_root(), &[]);
     assert_eq!(out.status.code(), Some(1), "ignored is exit 1");
     let err = String::from_utf8_lossy(&out.stderr);
     assert!(
@@ -179,12 +286,17 @@ fn sigint_helper_reports_error_and_never_ignored_when_the_probe_cannot_run() {
 #[test]
 fn gate_refuses_to_start_when_sigint_is_ignored() {
     let root = tempfile::tempdir().expect("tempdir");
-    let out = under_ignored_sigint(&format!(
-        "cd {} && PMACS_GATE_TARGET_ROOT={} {}",
-        repo_root().display(),
-        root.path().display(),
-        gate().display()
-    ));
+    // `--self-test`, NOT the ordinary gate. If the guard ever regresses,
+    // this row must not launch eight real gate stages inside the gate
+    // suite — the recursion constraint this file opens with. Self-test
+    // drives the same runner over a hardcoded synthetic plan, so the
+    // negative path stays bounded whatever the guard does.
+    let out = under_ignored_sigint(
+        &gate(),
+        &["--self-test"],
+        &repo_root(),
+        &[("PMACS_GATE_TARGET_ROOT", &root.path().display().to_string())],
+    );
     assert_eq!(
         out.status.code(),
         Some(1),

tests/gpu_invocation_acceptance.rs

@@ -190,21 +190,93 @@ mod crdt {
     /// helper's own stderr. A helper that cannot be executed is an
     /// `error` at this boundary, never evidence that `SIGINT` is
     /// ignored.
-    fn require_sigint_deliverable() {
-        let helper = Path::new(env!("CARGO_MANIFEST_DIR")).join("scripts/check-sigint-deliverable");
-        let out = match Command::new(&helper).output() {
+    /// The diagnosis for one helper invocation: `Ok` to proceed, `Err`
+    /// with the message a caller should fail on.
+    ///
+    /// Split from the assertion so the message itself is testable.
+    /// A6 requires this consumer to distinguish `error` from `ignored`,
+    /// and a diagnosis reachable only through a panic in a test that
+    /// cannot run under the condition it describes is not a witness.
+    fn sigint_diagnosis(helper: &Path) -> Result<(), String> {
+        let out = match Command::new(helper).output() {
             Ok(out) => out,
-            Err(error) => panic!(
-                "precondition undecidable: could not execute {}: {error}",
+            // Failure to execute the helper is an `error` AT THIS
+            // BOUNDARY, never evidence that SIGINT is ignored.
+            Err(error) => {
+                return Err(format!(
+                    "precondition undecidable --- could not execute {}: {error}",
                     helper.display()
-            ),
+                ));
+            }
         };
-        if !out.status.success() {
-            panic!(
+        if out.status.success() {
+            return Ok(());
+        }
+        Err(format!(
             "precondition failed --- this is NOT a teardown defect.\n{}",
             String::from_utf8_lossy(&out.stderr).trim_end()
-            );
+        ))
     }
+
+    fn sigint_helper_path() -> PathBuf {
+        Path::new(env!("CARGO_MANIFEST_DIR")).join("scripts/check-sigint-deliverable")
+    }
+
+    fn require_sigint_deliverable() {
+        if let Err(diagnosis) = sigint_diagnosis(&sigint_helper_path()) {
+            panic!("{diagnosis}");
+        }
+    }
+
+    /// A6, R-d consumer: the direct test distinguishes `error` from
+    /// `ignored`, and neither message claims a teardown defect.
+    #[test]
+    fn rd_precondition_distinguishes_ignored_from_error() {
+        // `safe` proceeds silently.
+        assert!(
+            sigint_diagnosis(&sigint_helper_path()).is_ok(),
+            "the foreground case must proceed"
+        );
+
+        let dir = tempfile::tempdir().expect("tempdir");
+        let stub = |name: &str, body: &str, mode: u32| {
+            let path = dir.path().join(name);
+            fs::write(&path, body).expect("write stub");
+            fs::set_permissions(&path, fs::Permissions::from_mode(mode)).expect("chmod stub");
+            path
+        };
+
+        let ignored = stub(
+            "ignored",
+            "#!/bin/sh\necho 'pmacs: SIGINT is ignored; run this command with SIGINT deliverable' >&2\nexit 1\n",
+            0o755,
+        );
+        let message = sigint_diagnosis(&ignored).expect_err("exit 1 must be refused");
+        assert!(message.contains("SIGINT is ignored"), "{message}");
+        assert!(
+            message.contains("NOT a teardown defect"),
+            "the whole point is not to read as a teardown defect: {message}"
+        );
+
+        let erroring = stub(
+            "erroring",
+            "#!/bin/sh\necho 'pmacs: could not determine whether SIGINT is deliverable (probe status 42)' >&2\nexit 2\n",
+            0o755,
+        );
+        let message = sigint_diagnosis(&erroring).expect_err("exit 2 must be refused");
+        assert!(message.contains("could not determine"), "{message}");
+        assert!(
+            !message.contains("SIGINT is ignored"),
+            "an undecidable probe is not evidence that SIGINT is ignored: {message}"
+        );
+
+        // Not executable at all: an `error` at the boundary.
+        let unrunnable = stub("unrunnable", "#!/bin/sh\nexit 0\n", 0o644);
+        let message = sigint_diagnosis(&unrunnable).expect_err("an unrunnable helper must refuse");
+        assert!(
+            message.contains("undecidable") && !message.contains("SIGINT is ignored"),
+            "boundary failure is undecidable, never ignored: {message}"
+        );
     }
 
     fn wait_for_exit(child: &mut Child, timeout: Duration) -> std::process::ExitStatus {