# GPU launcher / probe SIGINT teardown — framing Revision 11. Status: **MECHANISM FOUND (§4c). Awaiting approval — the problem statement has changed, so the remedy in §7/§8 no longer follows.** Revision 10 was approved 2026-08-19 at `4fba9f6`, authorising diagnostic-only D1/D2. They ran, and found the mechanism on the first reproducing sweep. It is not what this document was built around: bet 1 is falsified, A5 is struck, and nothing is wrong with the probe's shutdown path. Revision 9 was approved 2026-08-19 at `15c25ec`. **That approval did not extend to revision 10**, because retiring D0b (§7) materially changed the approved diagnostic sequence — the revision 9 text made D0b mandatory before every other diagnostic. Revision 10's approval covers that retirement and the A3 contingency that preserves its obligation. D0a's execution and result (§4b) are reported; D1/D2 are authorised but have not started. Revisions 1 and 2 were each rejected on five findings. Every correction is recorded in place rather than quietly rewritten, because three of them were claims this document itself had advanced: - r1 → r2: the ">6 s selector" and the "≥8 s lifetime" arithmetic (§5); "two processes with default disposition" (§3); "119 binaries green, one red" (§1); an unobtainable A2 (§8); "journey steps touched: none" (§9). - r2 → r3: **"R9 ran the same binaries" — it did not** (§4); "the probe never blocks indefinitely" (§3); the launcher call-site count (§5); reduction provenance, now in `docs/probe-sigint-evidence.md`; and ledger corrections that had not been made portable (§11). - r3 → r4: the interaction table overstated (§4); the red count was 7, not 5, and abbreviated argv were not argv (manifest); "workspace artifact family" conflated Cargo suffix with byte identity (manifest); ledgers still carried the falsified R9 conclusions (§11). **And a finding that reframes the lane: the failure has a datable onset (§4a) and is not long-standing.** - r9 → r10: **D0b retired as a precondition** (§7), which changes the approved sequence and is why this revision needs its own approval; D0a executed and its causal conclusion narrowed twice — "source hypothesis eliminated" withdrawn in favour of "the commits do not discriminate under current conditions" (§4b, and the endpoint table's two uniform-same rows); portable provenance corrected after it corrupted every log digest and silently dropped `/tmp` and `MemAvailable`; and `uptime` recorded as **UNKNOWN**, since §7 names it but the harness kept only the load averages. - r8 → r9: D0a's classifier was not total — it named only "clean split" and "mixed", leaving both-green, both-red, non-execution, copy-disagreement and unrelated-failure outcomes unprescribed, all of which occur in the historical logs (§7); and strict A/B/A/B does not equalise drift (§7). - r7 → r8: the superseded one-run D0 rule survived in three places (§4a, §7, manifest, ledger); D0a still overstated its rates and left the bisect's own classifier unspecified (§7); residual artifact wording and four wrong suffix attributions (§4, manifest). - r6 → r7: the ancestry supports **no** causal statement at all — the observations are non-comparable, and even "outcome is not determined by commit alone" is withdrawn (§4a); D0a was not yet a valid decision procedure (§7); "neither binary contains signal-handling code" is false — the `pmacs` binary registers SIGINT in daemon mode (§3); residual artifact wording (§4, manifest). - r5 → r6: the ancestry argument overreached (§4a) — it shows outcome is not determined by commit alone, and nothing more; residual byte-identity and "artifact family" wording in both ledgers (§11); and three provenance slips (§4, manifest). - r4 → r5: the section summaries still carried revision-3 counts and groupings (§4); the onset count was 13/1/3, not 14 (§4a); "byte- different" overstated what is knowable about historical artifacts (§4, manifest); and **the onset is not a source boundary** (§4a). ## 1. The problem, stated as what is observed `ctrl_c_on_launcher_group_does_not_reach_spawned_daemon` fails with ``` child did not exit within 5s (tests/gpu_invocation_acceptance.rs:180, called from :1115) ``` The test spawns `pmacs --gpu --socket ` in its own process group (`process_group(0)`, `:1107`), waits for the probe to report `phase=ready`, sends `SIGINT` to the **group** (`:1113`), and requires the launcher to exit within five seconds. **It fails in two binaries, not one.** `tests/gpu_initial_target_acceptance.rs` includes the suite as a module, so a reproducing sweep reds twice. Reference run `20260816T064549Z-2144707/09-sweep-crdt.log`: | | line | result | |---|---|---| | `gpu_initial_target_acceptance` | 3097 | `FAILED. 14 passed; 1 failed … 5.19s` | | `gpu_invocation_acceptance` | 3131 | `FAILED. 14 passed; 1 failed … 5.18s` | | green result summaries | — | **119** | So the correct statement is **119 green result summaries and two red binaries**. Revision 1 said "119 binaries green, one red", which was wrong on both halves. **This is pre-existing on `main`.** The identical `build-crdt && sweep-crdt` pair at `72da24a`, clean worktree, own target directory, fails the same test. ## 2. Why this blocks more than one lane `sweep-crdt` is stage 15 of the sixteen-stage `--protocol` gate. While it reds, **no branch can present a green gate**, `main` included. `panel-mapping-generation` (§5b) is complete with its own fifteen stages green and is held behind this lane by explicit instruction. ## 3. Ground truth (cited), and what it does *not* establish - **`run_gpu`'s own path installs no handler.** It (`src/main.rs:324`) blocks in `command.status()` (`:363`) — a plain `waitpid` — with nothing installed along the way. Grepping `SIGINT|signal_hook|sigaction|ctrlc|set_handler|pthread_sigmask|sigprocmask` across `pmacs-gpu/src` returns nothing. **Revision 6 said "neither binary contains signal-handling code"; that is false.** The `pmacs` binary *does* — `install_signal_handlers` (`src/daemon.rs:628`) registers `SIGINT` and `SIGTERM` — it simply is not on `run_gpu`'s path. And a grep of project sources cannot exclude a runtime or dependency installing a disposition. So the established fact is narrow: **no explicit installation on `run_gpu`'s path**. - **The probe's event loop wakes at least every 50 ms.** `run_headless_managed_probe` (`pmacs-gpu/src/main.rs:1065`) loops on `event_rx.recv_timeout(Duration::from_millis(50))`. **Revision 2 said "never blocks indefinitely", which is false**: the probe's stdin reader thread blocks in `read_to_end` (`:1109`) with no timeout, and once `ready` the loop has **no deadline of its own** — it leaves only when stdin closes (`:1212`). So the process is not bounded; only the event wakeup is. - **The daemon *does* handle signals, deliberately.** `src/daemon.rs:629-641` registers `SIGTERM`/`SIGINT` via `signal_hook::flag`. The daemon is the process the test asserts must **survive**, detached from the launcher's group. **Correction to revision 1.** Revision 1 concluded from the first two bullets that "two processes with default `SIGINT` disposition should both die at once". **That does not follow, and it contradicted this document's own leading hypothesis.** Absence of handler *code* says nothing about runtime *disposition*: `SIG_IGN` is inherited across `fork` **and** survives `exec`, so either process can hold a non-default disposition it never installed — from the test harness, from `cargo`, or from the invoking shell. Inherited ignore is a live candidate precisely because `run_gpu`'s path is silent. But **"whatever disposition they hold was inherited" is a hypothesis, not a finding** — revision 6 stated it as established, which it is not, since neither a source grep nor an absent call proves what the runtime disposition is. D2 measures it. Until then it is one candidate among the three D1/D2 are built to separate. ## 4. Reductions attempted **Full provenance lives in `docs/probe-sigint-evidence.md`**, which is pushed with this branch: exact command, worktree, HEAD, cleanliness, the Cargo suffixes actually executed, result, and log digest for every physical run. Log bodies stay machine-local under `/home/jeans/build/pmacs-gate-targets/probe-sigint-evidence/` — `/tmp` is a tmpfs and they were nearly lost to a cleanup mid-lane. Three provenance caveats are recorded there rather than smoothed over: **R1 and R2 have no preserved log** (revision 2 cited `gpu3.log` for both R2 and R6; that log is R6's three-suite run alone, and counting one run as two was wrong); **cleanliness is `UNKNOWN` for every pre-manifest run**, because it was not recorded at the time and is not inferrable; and **R1–R10 ran in the `panel-mapping-generation` worktree**, not at `main`. `D0` re-runs the matrix under a harness that captures all of it, at `main`, before any row here is relied on. All rows carry `--features crdt`. Full argv, worktree, HEAD, cleanliness and Cargo suffixes per run: `docs/probe-sigint-evidence.md`. | # | reduction (after `cargo test`) | runs | result | log | |---|---|---|---|---| | R1 | `--test gpu_invocation_acceptance ctrl_c_on_launcher_group` | 3 | green, 0.15–0.17 s | **no log preserved** | | R2 | `--test gpu_invocation_acceptance` (whole suite) | 1 | green, 15 passed | **no log preserved** | | R3 | `--workspace --no-fail-fast -- --skip basedpyright ctrl_c_on_launcher_group` | 1 | green — every binary runs, only this test executes | `filtered.log` | | R4 | `--lib --test gpu_invocation_acceptance --no-fail-fast` | 1 | green, 2145 + 15 | `two.log` | | R5 | `--test gate_script_acceptance --test gpu_invocation_acceptance` | 1 | green | `suspect.log` | | R6 | `--test gpu_font_acceptance --test gpu_initial_target_acceptance --test gpu_invocation_acceptance` | 1 | green | `gpu3.log` | | R7 | `--lib --bins` + `--test`×14 (targets 6–19) + the suite | 1 | green | `half1.log` | | R8 | `--test`×18 (targets 20–37) + the suite | 1 | green | `half2.log` | | R9 | `--lib --bins` + `--test`×32 (targets 6–37) + the suite | 1 | green (`-91f51d0b`, `-6b4b8223`) | `prefix.log` | | R10 | `--workspace ... --test gpu_initial_target_acceptance --test gpu_invocation_acceptance` | 1 | green (`-5d9105cb`, `-d4dae4f0`) | `wsonly.log` | | F1–F7 | full `--workspace --no-fail-fast -- --skip basedpyright`, plus three gate `sweep-crdt` stages | **7** | **red, 7/7** | `base-sweep.log` (at `72da24a`), `postclean.log`, `sweep-inst.log`, `sweep-diag.log`, gates `…-1977433`, `…-2144707`, `…-2375685` | **Correction to revision 2: R9 did not run the same compilations.** It executed `gpu_invocation_acceptance-6b4b8223dea45247`; the failing sweeps executed `-d4dae4f01bcdef62`. **Differing Cargo suffixes mean Cargo computed different metadata hashes — different compilations.** Revision 4 went further and called them "byte-different"; that is **withdrawn**, because the bytes a historical run executed are not knowable now — target directories have been overwritten, and a hash computed today is the hash of the current occupant. The weaker claim is sufficient: R9 establishes **same target names and order**, not the same compilations. What the evidence is **consistent with** is an interaction. It does not isolate one, because the rows differ in more than the two columns shown — different source heads, different worktrees, unknown cleanliness, and different Cargo compilations: | prior targets execute | compilation set | result | |---|---|---| | yes | `-91f51d0b` + `-6b4b8223` (`prefix.log:3066`, `:3087`) | R9 green | | no | `-5d9105cb` + `-d4dae4f0` (`wsonly.log:3`, `:24`) | R10 green | | yes | `-5d9105cb` + `-d4dae4f0`, all seven | **F1–F7 red (7)** | Neither factor alone reproduced it **in these runs**. That is the whole of the claim. `--workspace` artifact selection is **not sufficient by itself and not ruled out**; later-selected packages can influence Cargo's build graph and fingerprints *before* their test executables run, so "their targets execute after the failure at line 3066" does not exonerate them — that claim is withdrawn. And since §4's own preamble says no historical row should be relied on until D0, **this table is a description of what was observed, not a finding**. Revision 3 asserted it as an interaction while simultaneously disclaiming its inputs, which cannot both be true. Also refuted, by measurement: machine load (red on a quiet box, load 2.77); tmpfs starving RAM (**tested by experiment** — `/tmp` 21 G → 1.2 G, available 27 G → 45 G, still red); leaked daemons (peak 58, +8 per sweep, green runs already at 46–60); inotify (47 of 1024). ## 4a. The onset is datable — and it reframes the lane `sweep-crdt` appears **17 times** in this target directory's gate logs. `ctrl_c` fails in **exactly the last three**, and passed — both copies, `... ok` — in the runs before them. Counted **per test copy** across the 17 `sweep-crdt` logs: | outcome | runs | |---|---| | both copies `... ok` | **13** | | **neither copy executed** — stage died compiling `pmacs` (`error[E0308]`), `…-708693` | **1** | | both copies `FAILED` | **3** (`…-1977433`, `…-2144707`, `…-2375685`) | Revision 4 said "14 runs, 11 green, 3 red on other tests" and that the earlier reds failed on unrelated tests. **Both wrong.** The count is 13 / 1 / 3, and one earlier non-passing run is a **compile failure that never reached either copy**. The two genuinely red-on-other-tests sweeps did execute `ctrl_c`, and it passed. **So the failure is not long-standing.** "Pre-existing on `main`" remains true — F1 at `72da24a` reproduces it — but "always broken" was never established and is now contradicted. Last green containing it: `20260815T185708Z`. First red: `20260816T063330Z`. The machine was not rebooted across that boundary. **But the onset is NOT a source boundary, and a Git bisect is not yet justified.** Reflog and commit times put HEAD at `7599661` during the last green — `3c06176` was committed 40 s after that run finished — and at `724b785` during the first red, since `5174f73` landed at 08:45:41, after that run ended at 08:42:01. **Cleanliness was captured for neither**, and the tree was under active edit throughout. So the window dates a **machine/worktree-state transition**, not two clean revisions. One further relationship is worth recording **only to say what it cannot support**: `72da24a` is an **ancestor** of `7599661` (verified by `git merge-base --is-ancestor`), yet `72da24a` fails today while `7599661` passed on 08-15. **These two observations are non-comparable** — they differ in commit *and* in environment *and* in time — so **no causal conclusion of any kind may be drawn from the pair**. Revision 6 read it as "outcome is not determined by commit alone". **That is withdrawn too**: different commits can deterministically produce different outcomes, and this document's own fix-then-regression scenario is an example. The pair supports nothing about determinism either way. **Revision 5 drew still more from it.** It said a source cause was "positively discouraged", that the ancestry "says to expect" equal endpoints, and that "whatever changed is environmental, cached, or uncommitted". None of that follows either. Nothing in the pair distinguishes: - an environmental change; - a source/environment interaction; or - a source fix landing before `7599661` and a regression landing before `724b785`. And an older ancestor outside the interval behaving badly is simply **irrelevant** to whether `7599661..724b785` contains a regression. The endpoints, under the N = 5 contract in §7 D0a, settle only **whether a bisect is currently justified** — not whether the interval contains a regression. Those are different questions, and D0a's outcome (both-uniform-red) answers the first and leaves the second open. (Revision 6 wrote "needs only that the two clean endpoints differ *now*", which is the superseded one-run rule; a bare difference decides nothing.) **This still supersedes the reduction matrix as the lane's first move**, as endpoint reproduction — which is a decision procedure, not a prediction. ## 4b. D0a result — the commits do not discriminate today Executed 2026-08-19 under the approved contract **with one departure, stated up front**: the contract's captured-conditions list names `uptime`, and the harness kept only the load averages from it. `uptime` is therefore `UNKNOWN` for all ten runs. Everything else held — 10 runs, counterbalanced `A B B A A B B A A B`, N = 5 per endpoint, clean detached worktrees, isolated target directories, `dirty=0` verified per run, **zero voids, zero splits** — and no classification depends on the missing field, so the verdict stands. D1/D2's harness must capture the full list. **A (`7599661`) uniform-red. B (`724b785`) uniform-red.** By the endpoint table this is *both endpoints uniform the same way*: the difference is **not captured by those two commits**. - **No bisect of `7599661..724b785` is justified UNDER CURRENT CONDITIONS**, and none will run. `7599661` passed inside `sweep-crdt` on 08-15 and fails 5/5 clean today, so the two commits **do not discriminate now**. - **That is the entire causal claim.** Earlier wording here — "the source hypothesis is eliminated", "the interval cannot contain the transition", "not reachable by source" — is **withdrawn**. Uniform-red today says nothing about 08-15: a historical source regression could be **masked** by a later environmental effect, or by a source/environment interaction under which both commits now fail. **Failing to discriminate is not the same as not differing.** - **The onset window is deprioritised, not excluded.** - **A reliable reproduction now exists** — 10/10 today across two commits, ~4 minutes per run. This is D0a's most useful product: **D1/D2 no longer wait on a rare event.** - One cheap negative on "what else changed": **no package activity in the window** (`/var/log/pacman.log`, 08-15 19:57 → 08-16 06:33; nearest 08-18). Not pursued further — with a reproduction in hand, direct measurement dominates archaeology. Per-run provenance: `docs/probe-sigint-evidence.md` §D0a. ## 4c. D1/D2 RESULT — the mechanism, and it is my own artifact **`SIGINT` was ignored by every process in the target group, because I launched the test runner in the background.** Captured at the moment of the test's own `kill`: ``` test parent pid 8252 SigIgn=0000000000001007 launcher pid 8281 ppid=8252 pgid=8281 SigIgn=0000000000001007 SigCgt=0000000000000440 wchan=do_wait probe pid 8284 ppid=8281 pgid=8281 SigIgn=0000000000001007 ``` `SigIgn=0x1007` is signals 1, 2, 3 and 13 — and **signal 2 is `SIGINT`**. The launcher's `SigCgt=0x440` is signals 7 and 11 only, Rust's SIGBUS/SIGSEGV handlers; there is no `SIGINT` handler anywhere. Every `SigPnd`/`ShdPnd` is zero and every per-thread `SigBlk` is zero, so this is **ignored** delivery, not **blocked** delivery. Launcher and probe share `pgid=8281`, so nothing escaped the group either. All three candidates D1/D2 was built to separate are thereby separated. `kill(-pgid, SIGINT)` is a **no-op for every member**. The launcher waits in `do_wait` for a child that was never told to stop, and the 5 s deadline fires. ### Where the ignore comes from — measured in both directions | invocation | child's `SigIgn` | `SIGINT` | |---|---|---| | foreground | `0000000000001000` | bit 12 only (SIGPIPE) — **deliverable** | | `setsid nohup … &` | `0000000000000007` | SIGHUP, SIGINT, SIGQUIT — **ignored** | A shell running a command in the background without job control sets `SIGINT`/`SIGQUIT` to `SIG_IGN` in the child; `nohup` adds `SIGHUP`. **`SIG_IGN` is inherited across `fork` and survives `exec`**, so it propagates shell → `cargo` → test binary → launcher → probe. ### The controlled experiment Same command, same tree, same target directory, minutes apart — only the invocation differs: | arm | invocation | both target copies | |---|---|---| | 1 | foreground | **ok** | | 2 | `setsid nohup … &` | **FAILED** | ### This invalidates most of this lane's investigation, and I caused it I adopted `setsid nohup … &` on 08-16 to stop the Bash tool's ten-minute cap truncating gate runs. **That is the "onset".** - **The subset-vs-full distinction was never real.** Every reduction I ran was foreground; every full sweep was backgrounded. The two variables were perfectly confounded, so §4's matrix measured my invocation method rather than the code, and R9's "paradox" dissolves. - **The 08-15 → 08-16 window** dates my method change, not the machine and not the source. - **D0a's both-uniform-red is consistent and was right** — its harness backgrounded both arms, so both were red; the cause was invisible to a comparison in which it did not vary. - **"Pre-existing on `main`" is true but trivial**: `main` fails the same way backgrounded and passes foreground. ### Consequences for the contract - **Bet 1 is FALSIFIED, and A5 is struck** under its own D4 condition. An interactive terminal does not ignore `SIGINT`, so Ctrl-C on a real `pmacs --gpu` session behaves correctly. This is not a defect a user can meet. - **The §7/§8 remedy no longer follows.** What remains is narrower and genuinely real: 1. **The gate must not be invoked so that `SIGINT` is ignored** — a runner practice, and the direct cause of all seven red sweeps. 2. **The test should not fail obscurely when its precondition is absent.** "child did not exit within 5s" sent this lane chasing a teardown defect for nine revisions. It should detect an ignored `SIGINT` and say so. Silently skipping is not acceptable — `scripts/gate`'s own comments record that self-skipping tests "void coverage silently". - **A3's subset/full obligation is discharged by explanation**, not by D0b: the difference was invocation mode, demonstrated in both directions. `#![forbid(unsafe_code)]` rules out `pre_exec`, so remedy 2 is a precondition assertion rather than a repair — but that is a design question for the next revision, not a decision taken here. ## 5. Two retracted claims, both mine, kept as warnings **Claim A — "mechanism located".** Reported the launcher blocked in `do_wait` on a probe child in `futex_do_wait`. **Claim B — the retraction of A.** Argued A was unsupported because the failing launcher "must live ≥ 8 s" while the sampler's longest-lived was 5 s. **Claim B's arithmetic is false.** Both reproducing binaries finish in **~5.19 s including the five-second timeout** (`:3097`, `:3131`), so `phase=ready` is reached in roughly a tenth of a second and the failing launcher lives about **5.1 s total** — squarely inside what the sampler observed. A ">6 s" selector would therefore have captured **nothing**, repeating the very sampling error it was written to correct. So A is **not** refuted by B. A remains **unproven for a different reason**: under `--features crdt` the suite spawns root launchers from **six** call sites — `:509, :534, :544, :574, :725, :1097`, all inside `#[cfg(feature = "crdt")] mod crdt` (`:88`). Eight `--gpu` arguments appear in the file, but `:38` and `:65` sit under `#[cfg(not(feature = "crdt"))]` (`:26`) and are compiled out of the failing configuration. Revision 2 said "five" while citing eight, which was wrong twice over. Six is the number; what matters is that it is more than one, so a launcher captured by command line alone cannot be attributed to *this* test. The `do_wait` / `futex_do_wait` pair is consistent with the failing instance and consistent with a healthy sibling, and nothing recorded distinguishes them. The standing lesson is now the opposite of revision 1's: **do not key on process age at all.** Key on identity. ## 6. Bets 1. **The failure is a real teardown defect** — a user pressing Ctrl-C on `pmacs --gpu` sees the same hang. **This is a bet, not a finding**, and the current witness does not reach the real GUI path: it goes through a wrapper script and `--headless-managed-probe` (`:1090-1093`), not a live wgpu frontend. Confirming or dropping this bet is D4 below. 2. It is **not** a timing margin. A green run finishes in 0.15 s against a 5 s deadline — 33×. Margins that large do not erode. 3. Therefore **raising the deadline is not a fix** and is out of scope. If the conclusion turns out to be that the deadline is wrong, that needs its own argument and its own approval. ## 7. First step — diagnostics keyed on identity, not age No fix is proposed; the mechanism is unknown. The first commit is diagnostic only, and it must **discriminate** the three live candidates: blocked delivery, inherited ignore, and an escaped or wrong process group. - **D0a — reproduce the onset endpoints CLEANLY** (§4a): `7599661` (last observed green) and `724b785` (first observed red), each checked out clean, each in its own isolated target directory. This is a **decision procedure with no predicted outcome**. One run per endpoint decides nothing: **so far** the failure has been observed only in the full sweep, which is a statement about what has been run, not a property established of the defect. The procedure is therefore specified rather than left to judgement: - **N = 5 full `sweep-crdt` runs per endpoint.** Five is a **predefined evidentiary threshold, chosen in advance so the outcome cannot be argued after the fact** — it does not "mathematically separate" anything. The historical 7/7 red and 13/13 green are **not endpoint-specific rates** and must not be read as such: of the seven reds only F6 ran at `724b785`, and of the greens only the last ran at `7599661`, both with **unknown cleanliness**. - **Counterbalanced order**, not strict alternation. Runs go in `AB BA AB BA AB` pairs, so neither endpoint systematically follows the other. Revision 8 claimed strict `A/B/A/B…` makes session drift "hit both arms equally"; **it does not** — under strict alternation B always follows A and owns the final time point. What counterbalancing buys is the removal of *systematic order confounding*; with an even run count one arm still holds the last slot, and that residue is accepted and stated rather than papered over. - **Identical captured conditions per run** — and D0a satisfied this list only **partially**: it captured everything below except `uptime`, keeping the load averages and discarding elapsed time. D1/D2's harness must capture the whole list. Same harness as D0b — argv, worktree, `git rev-parse HEAD`, `git status --porcelain` emptiness, the Cargo suffixes executed, result, log digest — plus the machine facts that have already misled this lane once (`uptime`, `free`, `/tmp` usage, leaked-daemon count). **Classifying a single run.** The unit is *the two copies of the target test* — `crdt::ctrl_c_…` and `gpu_invocation_acceptance::crdt::ctrl_c_…` — and nothing else in the sweep: | run outcome | definition | |---|---| | **green** | both copies executed and both `... ok` | | **red** | both copies executed and both `FAILED` | | **split** | both executed, copies **disagree** | | **void** | either copy **did not execute** | Two of these are not hypothetical. `20260815T182846Z-708693` is a **void**: the stage died compiling `pmacs` (`error[E0308]`) and neither copy ran. And sweeps red on *unrelated* rows are ordinary — `…-2839374` and `…-830195` both failed other tests while both target copies passed. **A sweep red only on unrelated tests is a `green` run** under this classifier, because the classifier reads the two copies and nothing else. Unrelated failures are still recorded, as evidence about environment stability. **Handling each outcome:** - **void** — discard and re-run, up to **3 voids across the whole procedure**. Beyond that the environment is too unstable to classify anything and D0a **stops**; that is itself the finding. - **split** — **stop immediately.** Two copies of the same source in different binaries disagreeing within one run is a distinct defect, and characterising it takes priority over the endpoint question. **Endpoint verdicts**, from 5 valid (non-void) runs each: *uniform green* (5/5), *uniform red* (5/5), or **mixed** (anything else). | `7599661` | `724b785` | conclusion | |---|---|---| | uniform green | uniform red | **clean split → bisect `7599661..724b785` permitted** | | uniform red | uniform green | clean split, **direction inverted** — a real difference, but it falsifies which endpoint was believed good; record loudly and re-examine the onset reading before bisecting | | uniform green | uniform green | **the commits do not discriminate under current conditions** → no bisect now; ask what else changed across the window. This does **not** exclude a source difference that current conditions mask | | uniform red | uniform red | **the commits do not discriminate under current conditions** → same. A historical regression masked by a later environmental effect, or a source/environment interaction, remains possible | | mixed | any | **intermittent under fixed source → no bisect**; back to D1/D2 | | any | mixed | as above | - **Permitting a bisect requires the clean-split row.** Every other row forbids one. - **The bisect itself uses the same classifier.** Every intermediate commit is classified by the identical N = 5 protocol under the same captured conditions; a commit that classifies **mixed** — or produces a **split**, or exceeds the void budget — **aborts the bisect** rather than being guessed, skipped, or rerun until it agrees. A bisect whose steps are cheaper than its endpoints would inherit exactly the weakness this contract exists to remove. - **D0b — RETIRED as a precondition on 2026-08-19, kept as a contingency.** It existed to make the §4 reduction matrix trustworthy so the subset-vs-full comparison could locate the mechanism *indirectly*. D0a has since produced a **reliable direct reproduction** (10/10 across two commits, ~4 min/run), and D1/D2 measure the mechanism itself. Sharpening an indirect instrument while a direct one is in hand is the wrong order of work. **The obligation is not discharged.** A3 still binds: if D1/D2 do not account for why every subset passed while the full sweep fails, **D0b runs before this lane closes**, and its result is recorded either way. Retiring it as a *precondition* does not retire the question. As written, the retired step read: re-run the §4 matrix, at `main`, recording the artifact hashes actually executed **at run time**. Revision 2's strongest claim collapsed because command shape silently changed the binary; no further reduction should be trusted until each row names the executable it ran. - **D1 — key on the PID this test records.** The test already owns `launcher.id()`. Capture around its own `kill`, not by scanning for age or command line. - **D2 — snapshot before *and* after the signal**, for the test parent, the launcher, and the probe: - `SigIgn`, `SigCgt`, `SigBlk` — **per thread**, from `/proc//task/*/status`, since `SigBlk` is thread-specific and a process-wide reading would hide a blocked delivery on the one thread that matters; - `SigPnd` and `ShdPnd` — a pending-but-undelivered `SIGINT` is exactly what distinguishes blocked delivery from ignore; - `PID`, `PPID`, `PGID`, `SID` for each — which settles whether the signal was even addressed to the right group, and whether anything escaped it. A post-failure snapshot alone cannot prove inheritance; the before/after pair is what makes the claim provable. - **D3 — run the full sweep under D1/D2 until the failure is captured *with* its diagnostics.** Only then propose a fix. - **D4 — settle bet 1 separately.** Establish whether a real `pmacs --gpu` session, not the wrapper/headless probe, reproduces the hang. The answer decides whether A5 is an obligation or is dropped. ## 8. Acceptance criteria for the eventual fix Written now so the fix cannot quietly become "make the test pass". - **A1.** The mechanism is stated and demonstrated, not inferred: a witness failing before the change and passing after, plus a mutation showing the witness bites its own clause. - **A2.** `sweep-crdt` green for **three consecutive full runs on the reviewed fixed head of this branch**. Not "on main" — that is unobtainable before this lane is approved, gated and merged, and revision 1 stated an impossible precondition. Post-merge confirmation on `main` is a follow-up, not a gate on the fix. - **A3.** There is no established "R9 paradox" to explain — R9 ran different Cargo compilations, so the comparison it appeared to make was never made. What A3 requires instead: **the demonstrated D1/D2 mechanism accounts for the subset/full difference, or D0b recreates that comparison under captured provenance before this lane closes.** In the first case, record the mechanism's explanation. In the second, whatever D0b shows is either explained by the fix or explicitly recorded as unexplained. A fix that greens the sweep without either path leaves the gap stated, not hidden. - **A4.** No deadline raised, no test skipped, retried, or serialised to obtain green. - **A5.** **Conditional on D4.** If bet 1 holds, this is unconditional: Ctrl-C on a real `pmacs --gpu` session tears down the frontend and leaves the daemon running. If D4 shows the hang is reachable only through the wrapper/headless path, bet 1 is dropped, A5 is struck, and the lane is recorded as gate-correctness only. ## 9. Coherence impact (`COHERENCE.md` §20) - **Journey step touched: 12(a), "closing is clean."** Ctrl-C teardown of a GPU session is exactly that step, whether or not its grade moves. **Revision 1 said "journey steps touched: none", which was false** — it reasoned from grade movement, which §20 explicitly warns against. - **Grade movement: none expected.** This restores a property that is supposed to hold, rather than opening a new one. - **Interaction islands: none added.** - **Config registry: not touched. Background-work attribution: not touched.** - Beyond step 12(a), what this lane restores is every *other* lane's ability to prove itself, since no branch can show a green gate while stage 15 reds. ## 10. Out of scope - Raising or removing the 5 s deadline (bet 3). - The ~10 daemons each sweep leaks — real, separately recorded, and not implicated: green runs already ran at 46–60 leaked daemons. - `gpu_initial_target_acceptance` including the suite as a module. It is why the failure reds twice, and it is a tidiness question, not a correctness one. ## 11. Record corrections owed to other ledgers A correction is not made until it is portable. Two were outstanding when revision 2 was reviewed, and both are closed by this revision: - **This branch's ledger** asserted that two default-disposition processes "should both die at once" and then withdrew that same claim further down. The assertion is removed; only the withdrawal and its reasoning remain. - **`panel-mapping-generation`** carried "119 binaries green, one red", the ≥8 s arithmetic, the "default action" claim and the ">6 s selector"; `779a6bd` corrected those. **It still carried more**, found on re-review: `--workspace` unification "refuted", R9 running the "same binaries", later packages that "cannot be implicated", and a cause "cumulative across the preceding 37 binaries". Revision 3's claim here that the held lane no longer transports falsified claims was **premature**; those are corrected now, and this section should be read as a checklist that has been re-verified rather than an assurance.