# GATE0 Probe-3 (#827) — Mos byte-scope-verify CO-ATTESTATION (v9 full-closure, env-isolated + bytecode-pinned)

**Principal:** Mos (orchestrator, merge authority for the mosaic-stack governance lane).
**Committed under a DISTINCT git identity** (`mos-orchestrator@mosaic.local`) — deliberately NOT the
`ms-lead-reviewer@mosaic.local` lane signer that authored the harness and the §3 review — so this
record stands as a *distinct-identity* co-attestation. See "Independence".

**Verify class:** independent provider-byte read (`git show <full-40>:path | sha256sum`) plus
source-level inspection of the executed mechanism and the v7→v9 delta. Not a re-build, not a re-run.
This SUPERSEDES the v7 co-attestation `e08ad03` (and its SUPERSEDED note `2ae379e`), which was
byte-clear on the v7 bar and was overtaken by homelab's third-principal FAIL @f609a449 (broker
env-isolation + executed-bytecode-cache) and the resulting B7/B8 bar.

## Package under attestation

| Artifact | Ref |
|---|---|
| Branch | `feat/827-gate0-probe` |
| Harness commit-40 | `1c34e3cb3172acdcd094e683e847d7c984afc96c` |
| Harness `p3_d4_focused_run.py` sha256 | `29e5c7bfbe1911b52984bd94c79036bb1200ee82588318367b13c2b1053a0103` (32725 B) |
| §3-review-v9 commit-40 | `e1c9a4682da2892ca5f5381012caffe1dd7b43a7` (parent == harness `1c34e3cb`, byte-stable; adds only the review `.md`; ms-secrev-828 authored) |
| Review path | `docs/compaction-refresh/reviews/GATE0-PROBE3-V9-LAUNCHERFIX-S3-REVIEW-v9.md` |

**Pinned closure (all 3 sha256 INDEPENDENTLY recomputed by Mos from git objects == pins == embedded harness constants):**

| Member | Source (commit:path) | Pin sha256 | Size |
|---|---|---|---|
| launcher `launch-runtime.py` | `f4008307:packages/mosaic/framework/tools/lease-broker/launch-runtime.py` | `e950e422…` | 4237 B |
| helper `lease_generation.py` | `f4008307:packages/mosaic/framework/tools/lease-broker/lease_generation.py` | `061625402f…` | 3769 B |
| broker `p3_generation_broker.py` | `23c0caca:docs/compaction-refresh/probes/p3_generation_broker.py` | `4db4fef1…` | — |

> `f4008307` (held WI-3 #830 gated head) is **not on origin** — recomputed launcher+helper from the
> local `stack-cr-wi3-revoke` worktree (HEAD == `f4008307`); broker from origin `23c0caca`.

## Findings — VERDICT: byte-scope + mechanism + hygiene **PASS** (v9 = v7 full-closure + B7 + B8)

The v7→v9 delta is **exactly 22 insertions / 2 deletions**, confined to the intended B7+B8+B6c
surface; every prior invariant is byte-stable (outside the delta) from the v7 verify.

**B7 — broker child env-ISOLATED (homelab finding 1 CLOSED).** `launch_verified_broker` (`:568`) now
passes `env=environment` (the strict allow-list, `:570`) — the ambient-`os.environ`-inheritance hole
is gone — AND runs the broker with `-I` (`:552`, isolated: ignores `PYTHON*`/user-site) + `-B`
(`:553`). Both children are env-controlled: the launcher was already `env=env` at `PiRpc` (`:53`).

**B8 — executed bytecode PINNED/SUPPRESSED (homelab finding 2 CLOSED).** `reject_pinned_bytecode`
(`:498`) raises `RuntimeError` fail-closed if a `__pycache__` dir or any `*.pyc` exists in the pinned
dir, and is called before **each** consumer (launcher `:535`, broker `:562`). Bytecode writes are
disabled via `PYTHONDONTWRITEBYTECODE=1` (`:729`) in the allow-list env **and** `-B` on both command
lines. No unpinned `.pyc` can be executed; only the pinned `.py` re-hash governs.

**B6c — launcher sibling-import PRESERVED (v8 regression FIXED).** v8 over-applied `-I` to the
launcher; on Py3.11+ `-I` implies `-P`, dropping the script dir from `sys.path[0]`, so the pinned
launcher's bare `from lease_generation import` (launch-runtime.py:15) would `ModuleNotFoundError`. v9
uses `-s` (`:514`) + `-B` (`:515`) on the launcher (NO `-I`) — neither touches `sys.path[0]`, so the
sibling import still resolves to `pinned/lease_generation.py`. **Mos empirically re-verified on host
Py3.11.2** (throwaway, not the harness): `-I` launcher → `ModuleNotFoundError`; `-s`+`PYTHONNOUSERSITE`
→ import OK. The launcher's env isolation comes from the `PiRpc` `env=` allow-list, NOT `-I`, so
dropping `-I` does **not** reopen B7. My earlier constraint-(c) assumption ("`-I` does not strip the
script dir") was FALSIFIED for 3.11+; the author≠reviewer gate (ms-secrev-828) caught it — recorded.

**B5 conjunction (load-bearing repair) — HELD, all three legs (byte-stable from v7):**
(a) materialized from pinned git-object bytes via `materialize_closure`/`git_object_bytes`, `sha256==pin`
fail-closed; (b) `pinned/` `mkdir(0o700)` + `O_EXCL|O_CLOEXEC` `0o600`, no writable window — now also
`reject_pinned_bytecode` closes the `.pyc` side-channel; (c) re-hash == pin IMMEDIATELY before each
exec, no interleaved yield: launcher re-hash (`:538`) → `return PiRpc(command,…)` whose `__init__`
first statement is `Popen` (`:50`); broker re-hash (`:563`) + helper re-hash (`:566`) → `Popen`
(`:568`) on the next line.

**B6 — single pinned helper, complete closure.** Broker gets `--generation-module {closure.generation}`;
launcher resolves `import lease_generation` to the sibling pinned copy via `sys.path[0]`.
`closure_import_guard` (`:351`, called `:433`) AST-rejects any non-stdlib import other than
`lease_generation`. Single broker: `launch_verified_broker` 1 def (`:543`) + 1 call (`:766`).

**Invariants (all INTACT):** BAR1 `GATED_WI_HEAD == f4008307` (`:36`) and `merge-base --is-ancestor
66b1e0a0 f4008307` = YES (file-backed `.state` revocation fidelity present); fidelity
`generation_source=='state-file'` (`:639`), `state_file_in_fixture_root` (`:641`),
`MUTATOR_UNVERIFIED` (`:650`), `STALE_GENERATION` (`:651`); `lease_anchor_registered` (`:593`);
`-O`-safe (0 bare `assert`); `--runs choices=(3,)` (`:838`); allow-list env (0 `os.environ.copy`);
ABSENT-sweep (`yolo`/`execRuntime`/`p3_bank`/`promote_p2`/`retry`) = 0; the only `shutil.copy2`
(`:708`) is the `.pi/agent` credential copy, not a closure copy.

**Closure = exactly 3 files, materialized inside the fixture root.** No path escapes the fixture temp
root; no live/default broker; `.state` fixture-bound. **R1 owner tripwire NOT tripped** — B7/B8
deepen isolation/binding of an already-authorized touch, they do not widen the touched surface.

## Independence

Substantive principal-independence of review-v9 is satisfied by an orchestrator-dispatched,
builder-distinct Opus SECREV (`ms-secrev-828`, byte-only, non-builder, non-Mos). The shared
`ms-lead-reviewer` git signer on harness+review commits is evidentiary, not substantive — resolved by
(1) this Mos co-attestation under a **distinct** identity (`mos-orchestrator`) and (2) a homelab
third-principal verify under its own distinct identity = three distinct-identity principals of record.
Shared signer = tracked fleet-infra tooling-gap (durable fix = per-lane distinct signers), not a blocker.

## Scope of this record — byte-clear, NOT fire-authorization

Producing probe evidence **executes** the Gate0 mechanism; a byte-clear is not a fire-authorization.
This clears **bytes / scope / mechanism / hygiene on the v9 (full-closure + B7 + B8) bar**. FIRE
remains gated on: **homelab third-principal re-verify** (4th round, own distinct identity) + **Mos
transparency-to-Jason** + **Mos explicit FIRE GO**. Until then: nothing banked, WI-3 #830 held at
`f4008307` (unmoved), C-hatch armed (materialized-closure rig still no-fire / wrong-value /
assertion-FAIL / isolation-FAIL → possible Case-C → STOP + escalate to Jason).

**Mos verdict: v9 full-closure + B7 + B8 byte-scope + mechanism + hygiene PASS. Co-attestation of
record — committed.**
