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+# Gate0 Probe-3 (D4) Observation-Fidelity — §3-Conformance Review v4
+
+**Verdict: ✅ PASS**
+
+## Pin (G1 — reviewed object, mandatory)
+
+- **Reviewed object = `484849387006ab5561798506fd6042ddbd5617de`** (harness commit, branch `feat/827-gate0-probe`, `mosaicstack/stack` @ git.mosaicstack.dev).
+- **Reviewed file:** `docs/compaction-refresh/probes/p3_d4_focused_run.py` — sha256 (pushed provider bytes, `-o FILE`, FULL-40 ref, verified before trust): `9095eab7a4ddf11bb92bb5971d49e1facad12f4692ce2081665b0af47cbe5098` (23698 bytes, no not-found sentinel). Worktree bytes at `48484938` re-hashed identical.
+- **Co-reviewed fixture broker:** `docs/compaction-refresh/probes/p3_generation_broker.py` (sha256 `fd5327d2e9a2808282cbc9c4a4ccef42d2a806482b27cc48035191b9b11607c8`).
+- **Traceability anchor (independently recomputed):** `GATED_LAUNCHER_SHA256 = e950e4224e280f16979d90cabb89aa1896c5ee28bed2df957e14d018d43cda82` equals the sha256 of `packages/mosaic/framework/tools/lease-broker/launch-runtime.py` at WI-3 #830 reviewed head `f400830738998db105107a2a4c69c7f2a2a6fd5d` (computed from two independent worktrees).
+
+## Independence (G2)
+
+Distinct Opus §3-conformance reviewer (Gate-16 author≠reviewer). I did not build this harness (author = ms-rev-826);
+I am not Mos. This verdict is my own; the author did not author or edit it. Byte review only — **ran nothing** (no
+harness, no broker, no sockets/state). Prior v3 PASS (`ace60667`, pinned `abd2791f`) is correctly **superseded**:
+pinning a pre-`66b1e0a0` ancestor made D4 an in-memory socket simulation (hollow gate). v4 requires
+mechanism-fidelity within isolation (Jason R1).
+
+## BAR1 — Traceability (evidence attests the SHIPPED WI-3 D4 mechanism)
+
+| Check | Result | Evidence |
+|---|---|---|
+| `GATED_WI_HEAD == f4008307` (not `abd2791f`) | ✅ | :33 |
+| Launcher pinned by git-HEAD **and** sha256 | ✅ | precondition :285-288 (`head != GATED_WI_HEAD` raise; `sha256(launcher) != GATED_LAUNCHER_SHA256` raise); sha256 independently == f4008307's `launch-runtime.py` |
+| Launcher bytes contain the file-backed mechanism | ✅ | precondition requires `register_anchor` :290, `initialize_runtime_generation(generation_file, generation)` :291, `generation-{session_id}.state` :294, `MOSAIC_LEASE_GENERATION_FILE` :295, `read_runtime_generation`+`bump_runtime_generation` in `lease_generation.py` :296-299; order `register < initialize < execute` :302-303 |
+
+## BAR2 — Fidelity (file-backed generation, not in-memory simulation)
+
+| # | Requirement | Result | Evidence |
+|---|---|---|---|
+| i | Extension bumps `generation-{sid}.state` via the real helper, not in-mem | ✅ | ext `lifecycle()` calls `broker({action:'bump-generation'})` at every post-start boundary (harness :200-205); broker `bump-generation` → `bump_runtime_generation(generation_environment(identity))` (broker :119-120) |
+| ii | Broker reads generation via `read_runtime_generation`, not an in-mem counter | ✅ | broker loads the pinned module (`--generation-module`, :52-54); `file_generation()` = `read_runtime_generation(...)` (:77-78); authorize-probe reads `current_generation = file_generation(identity)` (:154); lifecycle `new_generation = file_generation(identity)` (:201). The in-mem `generations` dict is only an old-value cache for the monotonic guard (:199-204), never the authorization authority |
+| iii | `assert_d4` observes the FILE-BACKED transition | ✅ | `state_file_source` = all records `generation_source=="state-file"` (harness :370-372); `state_file_drives_lifecycle` = state-bumps == lifecycle generations[1:] (:368-369); `new_generation_unverified→MUTATOR_UNVERIFIED` :382; `prior_generation_stale→STALE_GENERATION` :383; `verified_revoked_on_reload` :380-381 — not a socket-only bump |
+| iv | `.state` bound to per-run fixture temp root | ✅ | broker `generation_environment` **raises if `state_path.parent != socket_path.parent`** (:73-74); `state_file_in_fixture_root` (:373-376); precondition forbids inherited `MOSAIC_LEASE_GENERATION_FILE` (:255-256) and requires socket in `gettempdir()` (:274-275); launcher/broker agree on `socket_path.parent / generation-{sid}.state` |
+
+## BAR3 — Carry-over
+
+| # | Result | Evidence |
+|---|---|---|
+| a LIVE-PATH (gated launcher @f4008307 at runtime, not released/plain execRuntime) | ✅ | Pi launched via `python3 <GATED_LAUNCHER> --runtime pi -- pi …` :502-505; `mosaic yolo`/`execRuntime` = 0 hits; register-before-exec producer in the invoked chain (precondition order gate) |
+| b Fail-closed precondition present+correct | ✅ | `gated_launcher_precondition` :250-306, invoked :485 **before** broker/Pi; raises on socket≠fixture / gen-file-inherited / write-path-escape / head-mismatch / hash-mismatch / not-register-before-exec-file-bound |
+| c Fixture-socket isolation, single p3 broker | ✅ | one broker Popen :486-500; `MOSAIC_LEASE_BROKER_SOCKET=socket_path` (fixture); direct launcher invocation ⇒ no default/XDG/`/run/user` fallback in path |
+| d `lease_anchor_registered` INTACT | ✅ | broker emits event + `session_id_shape=="hex-256"` (:102-107); `record_where` requires it (:324-326); `lease_anchor_fixture` check (:379) — not deleted/softened/optional/repointed (not Case-C) |
+
+## BAR4 — Homelab Gate-B carry-forward findings
+
+| # | Result | Evidence |
+|---|---|---|
+| b4-1 gated launcher @f4008307, not released/plain execRuntime | ✅ | :502-505; 0 `mosaic yolo`/`execRuntime` |
+| b4-2 **affirmative no-escape** (allow-list base, not deny-list) | ✅ | `isolated_environment` builds the child env from a **literal allow-list dict** (:442-461), NOT `os.environ.copy()`; only PATH/LANG/TERM/PI_CODING_AGENT (non-write-bearing) pass through; every write-bearing var (HOME/XDG*/TMPDIR/MOSAIC_AGENT_WORKDIR/HEARTBEAT_RUN_DIR/MOSAIC_HOME/D4_PI_LOG/socket) redirected under `root`; precondition double-checks each is `is_relative_to(root)` (:257-273). No unnamed/future inherited var survives |
+| b4-3 `--runs` exactly 3, fail-closed otherwise | ✅ | `add_argument("--runs", type=int, default=3, choices=(3,))` :591 (argparse rejects any other value) |
+| b4-4 cleanup try/finally spans the whole launch | ✅ | `broker=pi=None` :479-480; `try` opens **before** precondition/broker/PiRpc :482; nested `finally` always closes pi then broker+socket even on early `wait_path`/`PiRpc` failure :571-585 |
+| b4-5 `-O`-safe integrity + derived PASS | ✅ | load-bearing checks in a `checks` dict; `if failed: raise AssertionError` :385-387 and `if not passed: raise` :388-390 (NO bare `assert` anywhere — grep-confirmed); PASS = `"PASS" if passed else "FAIL"` derived from `all(checks.values())` :393, re-derived+checked in `run_once` :550-553 |
+
+## MUST-BE-ABSENT sweep
+
+`P5` / `P6` / `P2-bank` / `retry-launder` / `mosaic yolo` / `execRuntime` / `run_open` / `atomic-observation` /
+`pi_gate0_run` = **0 hits** (both files). Extension invokes only `bump-generation` / `lifecycle` /
+`authorize-probe` / `promote-probe`. No live/prod/real-broker path (single fixture broker; allow-list env; launcher
+pinned to fixture socket). No `.state`/gen-file path outside the fixture temp root (broker `generation_environment`
+raises otherwise). §4 live effect: none. No extra broker/socket beyond the single p3. No exec-at-import (both files
+`__main__`-guarded). Mechanism change is confined to the mandated R1 observation-fidelity deepening + BAR4 hardening;
+no scope-widen of what the probe touches.
+
+## Observations (transparency — not findings)
+
+1. The fixture broker retains a **dormant `source-invalid` action** (:179-194, P5-adjacent, in-mem). It is
+   **never invoked** by the harness or its embedded extension (verified: extension actions are only
+   bump/lifecycle/authorize/promote), and `assert_d4` never observes it — so the probe does **not** exercise or bank
+   P5. Pre-existing shared-fixture code, unchanged. Surfaced so Mos may, if desired, apply a stricter
+   purge-dormant-P5-from-the-fixture standard; under the "what the probe TOUCHES/does" framing it is not a violation.
+2. Fixture `HOME` receives a **read-only copy** of the operator's `~/.pi/agent` `settings.json`/`auth.json`/`bin/fd`
+   (:430-440, `shutil.copy2` into the fixture) so real Pi can authenticate to the model provider. It reads operator
+   state; it does not write/mutate operator HOME and does not emit/log credential material. Confined to the fixture.
+
+## Verdict
+
+**PASS @ `48484938`** — BAR1 (traceability to shipped f4008307 mechanism) + BAR2 (genuine file-backed generation,
+i–iv) + BAR3 (live-path / fail-closed precondition / isolation / intact assertion) + BAR4 (b4-1..b4-5) all hold,
+with zero out-of-scope surface exercised. The v3 hollow-gate (ancestor pin, in-mem simulation) is structurally
+closed: evidence now attests the shipped WI-3 D4 file-backed generation mechanism, launcher pinned by head+sha256,
+child env write-confined by allow-list, integrity `-O`-safe with a derived PASS.
+
+**Findings: none.**
+
+## Scope reminder (not a finding)
+
+Per §3/§5 of the amendment, producing this evidence **executes** the Gate0 mechanism. This review clears the
+**bytes**; **FIRE remains separately gated on Mos's explicit post-clear GO** and is not authorized by this review.
+
+---
+
+**Reviewer:** independent Opus §3-conformance reviewer (Gate-16 author≠reviewer). Byte review only; ran nothing.
+**Reviewed object (pin):** `484849387006ab5561798506fd6042ddbd5617de` · harness sha256 `9095eab7a4ddf11bb92bb5971d49e1facad12f4692ce2081665b0af47cbe5098`.