feat(compiler): add offline advisory consultation packets

[joehertel]

Why

This adds a narrow way to consult an external reviewer during implementation or validation without making model access part of compilation.

The compiler emits a deterministic, digest-bound request packet. A separate process may obtain advice offline, and Weft can validate the returned packet. Advice remains non-executing and non-authoritative.

CONTRIBUTING.md asks larger compiler changes to start with an issue. I am opening this as a draft so the exact implementation is reviewable, not asking for merge yet. If an issue-first discussion is preferred, I am happy to move the design conversation there.

This targets mvp because the implementation was built and tested against mvp@786bf97ae5a842452b69c900b785c8ee35c7d0a5.

What changed

• add closed request and response schemas with canonical SHA-256 binding
• bind source and definition digests plus normalized repository-relative locators
• require immutable read-only, no-canonical-write, and no-side-effect constraints
• require provider/model provenance and exact request binding on responses
• reject malformed JSON, unknown fields, weakened constraints, unsafe paths, digest mismatches, and invalid status semantics
• require findings for advice and blocked; forbid findings for abstain
• add deterministic disabled, not-configured, unavailable, and timeout outcomes
• add weft-codex-consult emit and non-executing verify commands
• document the offline protocol and non-goals

Safety boundary

This PR does not:

• dispatch a model
• access the network from Weft
• launch a process or runtime
• execute or automatically apply advice
• write canonical state
• install or wire a Codex runtime

Validation

• cargo test -p weft-compiler --test codex_consultation
• cargo test -p weft-compiler --test codex_consultation_cli
  • 11 passed, 0 failed
• cargo test -p weft-core -p weft-compiler --locked
  • 711 passed, 0 failed, 3 ignored across 11 result blocks
• source-fidelity audit: exactly 3 modified tracked paths and 5 new paths
• patch reverse-check passed; forward application to a fresh pinned export reproduced all 8 changed files byte-for-byte with core.autocrlf=false

Clippy disclosure

cargo clippy -p weft-compiler --lib --bins --tests --locked --no-deps -- -D warnings remains nonzero on existing workspace diagnostics. The captured run reported no diagnostics in the consultation-owned source, binary, or test paths.

Review focus

I would especially value feedback on whether this packet boundary belongs in weft-compiler, and whether blocked requiring at least one explanatory finding is the right closed semantic.