[bench] security: stop cross-project ledger leak, retire contaminated chain, add disclosure policy

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What

Started as "add a SECURITY.md." Surfaced a live leak: this public repo was
publishing source code from unrelated private projects. Four commits: stop the
leak, minimize what the ledger records, retire the contaminated chain under a
bounded constitutional amendment, and add a regression guard.

1. The leak

Bench's hook is registered globally in ~/.claude/settings.json, so it governs
every project on the machine. But ledger/chain.py pinned the ledger to the
Bench install directory, so every governed edit anywhere appended its full
diff into this public repo's chain.

	Entries	Foreign	Size	Diff bodies
Already public	490	264	4.4 MB	705
Uncommitted	1,882	1,715	17.8 MB	2,313

Exposed: another project's src/, an Electron app, a Next.js billing app,
.claude/plans/, project memory notes, the global settings.json. Scanned for
12 credential classes; every hit was fixture data, so nothing needs rotating.

Fix: resolve_ledger_path() routes by the project being governed.
BENCH_LEDGER_PATH wins; else a cwd inside the Bench repo uses Bench's own
ledger; else <project>/.bench/bench-ledger.json. load_ledger,
verify_chain, and the viewer all default to the same resolver, so the auditor
can never inspect a different file than the writer appends to.

2. Redaction of out-of-project bodies

Routing fixes other projects' sessions. A file edited from a Bench session
still lands here, so out-of-project diff bodies are now stripped before hashing:
content, old_string, new_string, edits, formatted_diff are dropped and
the entry is marked redacted. Path, tool, and verdict survive, so the audit
trail still shows the file was governed and how it was ruled on.

Classification and routing share one _project_root() anchor. They previously
disagreed: editing utils/api.py while sitting in tests/ would have been
judged external and stripped evidence from Bench's own record.

Residual, stated plainly: judge prose may still quote a few lines of the change
it reasons about. This removes the systematic copy of file bodies, not every
possible quotation.

3. C-008 amended, chain retired (constitution v2)

Bench vetoed its own chain reset under C-008, correctly: removing a ledger
is deletion. Its proposed alternatives (keep the contaminated chain in-repo, or
append to it) both leave 1,715 foreign diffs in a public repo. C-008 and the
privacy requirement genuinely conflicted, so the law was amended rather than
circumvented.

Retirement is now permitted with one trigger (the chain contains content that
must not be published) and four mandatory elements: a human decision that is
never agent-initiated, an archive passing verify_chain before the original
moves, an anchor recording tip hash, genesis hash, entry count, timestamps,
verbatim archive path and reason, and indefinite retention. Editing, reordering,
or removing an individual entry remains forbidden with no exception.

A first draft of the amendment was itself vetoed under C-007 for being
open-ended and unenforceable. The landed version names the authority, defines
the verification step, and gives auditors a concrete check.

The retirement then ran:

retired entries : 2471 (2026-04-22 to 2026-07-24)
tip hash        : 2176516fec72f66da131096438cd318d8453409f87dec30107a312beef7a4c8d
anchor entry    : 7a06ce4f-aa12-4129-ada3-d200ece60cdb

The auditor check C-008 prescribes was run against the result: the archive
verifies valid at 2471 entries, and its tip hash, genesis hash, and entry count
all match the anchor. Auditable, not asserted.

ANCHOR verdicts are plumbed through stats and the CLI so retirement markers
never skew the pass rate. Dry-run confirmed verify, stats, and the HTML viewer
handle the new entry shape without erroring.

4. Regression guard

tests/test_ledger_hygiene.py asserts no ledger entry carries a diff body under
a non-relative path. Verified non-vacuous: run against the retired chain it
reports 349 violations, so it would have caught this in April.

Deliberately stricter than the runtime redactor: it flags any absolute path,
including one pointing inside the repo, since that means either foreign source
or a path-normalization regression. Absoluteness is matched by regex, not
os.path.isabs, because CI runs on Linux where isabs(r"C:\Users\...") is
False and a Windows-shaped path is exactly what the guard exists to catch.

5. SECURITY.md and CI hardening

Policy written against Bench's real threat model. In scope: governance
bypass, fail-open regressions, ledger forgery that still passes cli verify,
prompt injection through governed content, credential exposure. Out of scope:
model judgment quality (a disagreeable Oracle verdict is a constitution issue,
not a CVE). States plainly that the ledger is tamper-evident, not tamper-proof.

• permissions: contents: read at workflow level
• actions/checkout v4 to v7, actions/setup-python v5 to v7 (aliases verified
  via the refs API; CI green on 3.11, 3.12, 3.13)
• dependabot.yml for pip and github-actions; alerts and security fixes enabled

Do not enable auto-merge on Dependabot PRs. That routes dependency changes
around the pipeline, which C-007 forbids.

Governance record

Bench governed every change here and rejected four of them:

1. VETO (C-004) on a bare Any annotation. Complied.
2. VETO (C-007) on the first constitutional amendment as unenforceable.
   Rewritten with a named authority and an auditor-executable check.
3. VETO (C-008) on the chain reset itself, before the amendment existed.
4. VETO (C-008(a)) on the retirement script, because the human decision was
   a narrative string authored by an agent. The gate is now structural, and it
   refused two non-interactive invocations from me before the owner ran it.

Plus one fail-closed VETO when a Defender stage errored, and Oracle catches
on a missing Path import, an unverified resolve_ledger_path import, and an
irreversible C-008 hazard in a test that would have written synthetic entries
into the real chain.

Testing also caught what review did not: the first isatty() human gate silently
failed under Git Bash, where msys reports a TTY even with stdin redirected. The
EOFError path is what actually holds.

Not fixed

tests/test_hook.py:371 has a pre-existing F841 (unused original_cwd), left
alone as unrelated. Ruff is not in CI.

Already-public history is unchanged by deliberate decision: 56 unique cloners
pulled this repo in the preceding 14 days, so a rewrite cannot un-distribute the
264 foreign entries, and severing the chain would cost more than it recovers.