argus: add ARGUS.md, wire it into the review prompt, raise max-turns to 70

[ohalushchak-exadel]

Summary

Adds a repo-root ARGUS.md that layers repo-specific priors on top of the base prompt at .github/ai-review/expert-adcp-reviewer.md. Deliberately scoped to invariants the base prompt does not already encode:

• fcap seller_agent_url read/write symmetry — PR trusted-match: bump adcp pin to 3.1.3 and close identity/context spec gaps #406 landed canonicalization on the reader side (via canonicalizeSellerAgentURL in targeting/identityagent/service.go). A new fcap.Field{...} construction that skips the helper fragments cap buckets by URL spelling and silently fails cap enforcement open.
• Router public endpoint surface + env-var contract — enumerates /registry/snapshot, /tmp/context, /tmp/identity and the TMP_* env-var prefix in cmd/router/main.go. The base prompt's MUST-FIX Add CI: build, test, lint, benchmark #6 covers the conventional-commit marker; ARGUS.md names the concrete surface it applies to.
• Schema regen — one extra check — after regen, the version comment at line 2 of adcp/types_gen.go must match adcp/schemas/VERSION. A drift means the regen ran against a stale bundle.
• Metrics error-label discipline — closed-set outcome labels ("timeout" | "canceled" | "error") on identity-agent and context-agent metrics, per targeting/identityagent/metrics.go and targeting/contextagent/metrics.go. Grafana-relevant.
• Explicit sync clause — every rule is a claim about repo behavior, so a diff that invalidates one must update ARGUS.md in the same PR. Written to be obvious to both human contributors and coding agents.

Sections that would have duplicated the base prompt or AGENTS.md (general TMP-signing MUST-FIX, protocol-managed-skills read-only rule, pinhole overview, generic high-risk-paths list) are deliberately omitted. Draft caught by a Fable-5 audit pass that flagged five duplicative sections and two BLOCKING trivial-path globs — see the commit for the trim rationale.

Workflow changes

1. Build Argus review prompt step now reads ARGUS.md if present and injects it into the prompt under a # Repo-specific context (from ARGUS.md) header before the pre-computed inputs. Missing file → no-op, existing behavior preserved.
2. Self-modification gate regex extended to include ^ARGUS\.md$. Argus pauses on this PR (and any future PR that edits ARGUS.md), which is intentional — a review agent must not approve changes to its own priors. CODEOWNERS gates the merge.
3. --max-turns raised from 60 to 70 to give the reviewer more room on the multi-hunk cross-file audits the current MUST-FIX list drives.

Test plan

• YAML change is structural bash-heredoc addition inside an existing string; verified by inspection
• Self-mod gate will fire on this PR — Argus should post the "🛑 Argus paused" comment, not a review. That is the expected behavior and validates the gate change.
• ARGUS.md content audited by a separate Fable-5 pass against the current tree: all cited paths and behaviors verified; duplicative content pruned

🤖 Generated with Claude Code

[aao-ipr-bot]

🛑 Argus paused on this PR.

This PR modifies Argus's own configuration (.github/workflows/ai-review.yml, .github/ai-review/**, or ARGUS.md). Argus will not post an approving review on changes to its own gates — a human reviewer must take this PR. CODEOWNERS already requires a human approval on these paths.

Workflow run

_{Automated by the Argus self-modification gate.}