fix(ci): bind remote fixture downstream source

docs/scratchpads/1050-install-state-machine-red-fixture.md

@@ -86,3 +86,61 @@ Implement C1 from the canonical greenfield-install PRD v2: a transactional P0–
 - Review-93 RED evidence at frozen `378bc1a`: isolated positive-control full-suite exit `1` with `P2 left an in-progress transaction`; isolated permission-failure attack full-suite exit `0` with final `installer next lane tests passed`. No binary shadowing or PATH interception was used; the failure came from a real target-owned mode-0100 directory.
 - Fix-round GREEN: `pnpm test:installer`, native next-lane, root/`ci-base:latest` next-lane, state-machine, verified-fetch, Bash syntax, ShellCheck, `pnpm typecheck`, `pnpm lint`, `pnpm format:check`, and `git diff --check` pass. The direct attack child exits 1 and names `P2 fault-state enumeration failed`. All 81 Mosaic Vitest files / 1508 tests pass under an isolated npm prefix; the wider framework-shell chain reaches the pre-existing #973 Bash-line-number gate and exits 97, matching the known host-specific condition rather than this delta. Codex code review approved at 0.93 confidence with zero findings; Codex security review reported no risk at 0.96 confidence with zero findings.
 - Sidecar GREEN locally: `sha256sum -c tools/install.sh.sha256` and the workflow's expected/actual comparison both resolve `e59cb441a2f37ae9150f8eae470238e9d858a1816df93343d9784a6796676096`. This is not substituted for the required immutable provider-fetch arm at the pushed head.
+
+## Round 3 — remote-arm downstream source binding
+
+### Objective and constraints
+
+- Tracking remains `mosaicstack/stack#1050`, delivery PR #1054, branch `feat/1050-install-state-machine-red-fixture`; `docs/TASKS.md` remains orchestrator-single-writer.
+- Bind the remote arm's downstream stack framework/source archive to the same immutable `${CI_COMMIT_SHA}` as the digest-verified `install.sh`, while retaining `--next` and its exact resolved CLI/gateway lane-version assertion.
+- RED first: the realised source commit/digest assertion must reject the existing stale `origin/next` substitution; GREEN must restore the exact expected `P6 FAIL` and pass the comparator. R7 then deletes the binding and requires RED again.
+- Fenced out: the expected-RED manifest (including `P6=FAIL`), #869 activation, and #1068 digest-before-comparator sequencing.
+- Push budget: one force-with-lease push pinned to provider head `ff3f0d29f1763bed44a60610d073036112e66b77`; run the queue guard first; do not poll CI after push.
+- Working estimate: 14K reasoning/output tokens; no external hard token cap. Scope reduction order: reuse the existing local-source archive seam, add one realised-state assertion, avoid installer behavior changes.
+
+### Corrected reference citation
+
+The transferable reference is only **the container-image acquisition path in `fa-install.sh`**: resolve mutable input once to `Docker-Content-Digest`, fail closed if unresolved, render `@sha256`, then verify running images against the resolved digest. It is not a claim about USC's installer as a whole; the sibling root bundle extraction in `Install-FieldAgentOnPanel.ps1:82` is unpinned. The applicable structure is `RESOLVE-ONCE -> PIN -> FAIL-CLOSED ON RESOLUTION -> VERIFY-AFTER`, applied per acquisition path.
+
+### Remote-arm acquisition-path census before the fix
+
+Code-path enumeration only; execution of the complete list is **NOT MEASURED** in this round yet. Logical payload paths are counted once even when one command is invoked repeatedly or installs a dependency graph.
+
+| # | Acquisition path taken by the arm | Pre-fix binding state | Scope disposition |
+|---|---|---|---|
+| 1 | Woodpecker checkout containing the workflow, fixture, sidecar, and comparator | CI commit checkout (commit-bound by runner contract) | existing arm substrate |
+| 2 | `node:22-bookworm-slim` step image | mutable image tag | unpinned sibling; outside this fix fence |
+| 3 | Debian package set acquired by `apt-get update/install` | repository-current, no package versions/snapshot | unpinned sibling; outside this fix fence |
+| 4 | remote `tools/install.sh` | exact `${CI_COMMIT_SHA}` URL plus checked SHA-256 | in scope; already bound first hop |
+| 5 | `@mosaicstack/mosaic@next` CLI package graph | mutable lane resolved to an exact top-level version, exact version installed, realised top-level version verified | lane assertion; must remain |
+| 6 | `@mosaicstack/gateway@next` package graph | later re-resolution wins and is verified against itself; drift from the first value can be silently accepted | partially constrained TOCTOU sibling; outside this fix |
+| 7 | `mosaicstack/stack` framework/source archive consumed by `ensure_monorepo` | `next` resolves once to `4df478cdd150fdf8d52ea109f02ade5d85017acd`, not the arm's CI commit | **in-scope defect; bind to CI commit** |
+| 8 | sequential-thinking MCP package warmed via unversioned `npx -y @modelcontextprotocol/server-sequential-thinking` | mutable package resolution | unpinned sibling; outside this fix fence |
+| 9 | Excalidraw npm dependency graph | shipped `package-lock.json` exact versions + registry integrity hashes; `npm install` consumes the lock | already lock/integrity-bound, separate from CI-source identity |
+| 10 | canonical skills repo cloned by `mosaic-sync-skills` | mutable default branch of `mosaic/agent-skills.git` | unpinned sibling; outside this fix fence |
+
+Pre-fix mechanism breakdown (do not blend unlike strengths): **2 / 10 intended-CI-commit-bound** (#1 checkout, #4 installer); **1 / 10 resolve-then-pin with comparison to the authoritative value** (#5 CLI); **1 / 10 partially constrained because verify-after compares #6 gateway to its later re-resolution rather than an authoritative pin**; **1 / 10 lockfile+integrity-bound** (#9 Excalidraw); **1 / 10 internally pinned to an immutable commit+digest but bound to the wrong arm identity** (#7 framework at `4df478cd`); **4 / 10 unpinned siblings** (#2, #3, #8, #10). The in-scope same-CI stack payload ratio is **1 / 2** (`install.sh` yes; framework/source no).
+
+Resolution-failure behavior is separately stated rather than hidden in the counts. For #5/#6, a metadata-resolution failure during P1 blocks before mutation. Later package metadata/install failure enters the documented source fallback, but that fallback consumes the immutable stack archive already resolved in P2; failure to resolve or fetch that source is fatal. For #5, the P2 CLI value is authoritative and a later realised mismatch blocks P3 and rolls back. For #6, no authoritative P2 gateway value persists; a later same-suffix gateway drift can be silently accepted because the later value is compared with itself. Changing that TOCTOU path is outside this fix. The new #7 path accepts the 40-hex CI commit directly, fetches only its exact commit URL, rejects failed/empty acquisition, computes and passes the exact body's digest through the existing local-source seam, and rejects any realised manifest commit/digest mismatch without falling back to `next`.
+
+Denominator corrections were sent to and accepted by the lane lead before implementation. Four expressly unpinned siblings make `7/10` impossible. Post-fix, the primary mechanism breakdown is **fully constrained 5 / 10** (#1, #4, #5, #7, #9), **partially constrained 1 / 10** (#6), and **unpinned 4 / 10** (#2, #3, #8, #10). The meaningful repaired ratio is **2 / 2 same-CI stack payload hops**. The fix does not increase coverage; it moves #7 from wrong identity to intended identity. Every census revision moved assurance downward under additional questioning, never upward, so the census is a lower bound on defects and an upper bound on assurance.
+
+### Implementation plan
+
+1. Add the realised source commit+archive-digest assertion and pass the expected immutable identity through the remote fixture; run the current stale-`next` mechanism and capture RED before changing acquisition.
+2. Fetch the stack archive from the exact commit URL once, fail closed on failed/empty acquisition, compute its digest, pass that exact body through the installer's existing local-source archive seam, and verify the manifest's realised `sourceCommit` and `sourceSha256` against those values.
+3. Run exact-source GREEN: require `P6 FAIL` values and a passing `next-git-present` comparator; run focused installer/baseline gates.
+4. R7: delete the binding in a temporary mutant, run the same assertion to RED, then restore and re-run GREEN.
+5. Independent code/security review, commit with command-scoped identity, queue guard, one force-with-lease push pinned to `ff3f0d29`; stop without CI polling and report `believed-fixed, pending jarvis validation`.
+
+### Executed outcome
+
+- RED-first stale substitution: fixture `rc=1`; realised source `4df478cdd150fdf8d52ea109f02ade5d85017acd` / `3e6d831efe13c3b2c0501507099d4a566af5abf877dacf85e5d7e4284d35e5c7` rejected against expected `ff3f0d29f1763bed44a60610d073036112e66b77` / `944c6db1b01b23c83169e6dc83e0d31262b1d24a2825270441745eb65c269c25`; comparator `rc=1`, 8/19 mismatches.
+- Exact-source reproducibility, N=5 identical final-tree executions: every run had fixture `rc=1`, `@mosaicstack/mosaic@next=0.0.50-next.2207`, P3 PASS, realised source `ff3f0d29…` / `944c6db1…`, SOURCE-CONTROL PASS, `installer_exit=1`, `done_claims=0`, P6 FAIL, and P9 FAIL. Comparator `rc=0` occurred 4/5 (19/19 checks; action-failure reason); comparator `rc=1` occurred 1/5 (18/19; dead hooks active count `2`). The rate is the finding; no comparator verdict is claimed.
+- Timings/load: runs 1–2 NOT MEASURED; run 3 rc1 elapsed 912s, load 7.79/7.51/8.93 -> 12.28/14.82/11.79; run 4 rc0 elapsed 938s, load 12.28/14.82/11.79 -> 9.84/15.18/13.83; run 5 rc0 elapsed 954s, load 9.84/15.18/13.83 -> 3.94/4.76/8.18. Load does not explain this sample monotonically.
+- The `P6=FAIL` row remains untouched; P6 failed 5/5 while its reason signal varied. No comparator widening was performed. Checkout-source control independently exhibited the rc1/dead-hooks outcome, but its reproducibility was not separately measured.
+- #869 out-of-scope finding: current `defaultSupervisorProbe` checks bundled supervisor artifact presence and a resolvable socket path, not socket existence. The 2000ms capability-probe timeout is a code-read hypothesis for variance, NOT MEASURED as causal.
+- Final-tree R7 deleted the three local-source binding exports temporarily. The realised source reverted to `4df478cd…` / `3e6d831…`, SOURCE-CONTROL failed against `ff3f0d29…` / `944c6db…`, and comparator `rc=1` with 8/19 mismatches. The subject file SHA-256 was `a93113565aa69f2c6f3d792b78251021bb3bbe3f7813d5fed547ab0099fa3b98` before mutation and after restoration.
+- Trust boundary: the exact-commit URL trusts the configured repository provider's authenticated commit-to-archive mapping. The computed digest pins transfer/consumption but does not authenticate against repository/TLS compromise; signed provenance remains the canonical PRD v2 §3 deferral. Initial Codex security review retained this as HIGH/CWE-494; no stronger claim or out-of-scope signing change was made.
+- Final baselines: Bash syntax, ShellCheck, `pnpm test:installer`, `pnpm typecheck` (45/45), `pnpm lint` (25/25), `pnpm format:check`, and `git diff --check` pass. Codex code review APPROVE confidence 0.92 with zero findings; after explicit trust-boundary documentation, security re-review risk NONE confidence 0.96 with zero findings. The initial HIGH trust-root finding remains recorded as the signed-provenance deferral.
+- Full evidence and named paths: `docs/reports/verification/1050-c1-fix-round/09-round3-source-binding.txt`.