feat(mcp): add lint_url full detail mode

[aram-devdocs]

Fixes #40

Summary

• Adds optional detail argument to lint_url, defaulting to compact output.
• Adds detail: "full" structured content using deterministic full JSON violation payloads.
• Enforces the 50 KB response cap for full-detail payloads and documents the new option.

Validation

• cargo test -p plumb-mcp — passed
• cargo test -p plumb-cli --test mcp_stdio — passed
• cargo check --no-default-features — passed

Note

The original remote branch gh-issue-40-lint-url-detail-full already existed at divergent commit 61ea2e5; this PR uses gh-issue-40-lint-url-detail-full-09a39d0 to avoid force-pushing over it.

[github-actions]

I have everything I need. Here is the review.

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PR Review: feat(mcp): add lint_url full detail mode + fix(mcp): address lint_url review feedback

Scope: 2 commits, 3 files changed (net +192 lines): crates/plumb-mcp/src/lib.rs, crates/plumb-cli/tests/mcp_stdio.rs, docs/src/mcp.md.

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1. Determinism — PASS

No new nondeterminism introduced. The new code paths call plumb_format::json, which: sorts violations by sort_key(), builds a stable serde_json::Map, and derives run_id from a SHA-256 hash of the canonical serialization — no wall-clock, no map iteration leaking.

The pre-existing SystemTime (line 38) and HashMap (line 34) are scoped to the config-file mtime cache and do not flow into any tool response. Those are not new in this PR.

clippy.toml bans SystemTime::now and Instant::now (not SystemTime field storage), so the existing usage is conformant.

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2. Workspace layering — PASS

plumb-mcp already depends on plumb-format. The new use plumb_format::{json as full_json, mcp_compact} at line 43 is within that pre-approved dependency edge. No diagonal or reverse dependencies introduced.

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3. Error handling — PASS

build_lint_url_result and build_full_lint_payload are private fns returning Result<_, ErrorData>. No unwrap/expect in library code. expect calls in mcp_stdio.rs tests are in #[cfg(test)] context and are explicitly allowed by clippy.toml (allow-expect-in-tests = true).

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4. Test coverage — PASS

Four new integration tests in mcp_stdio.rs:

• mcp_lint_url_explicit_compact_matches_default — parity between default and explicit compact.
• mcp_lint_url_full_returns_json_envelope — happy path for full mode; checks plumb_version, run_id prefix, summary.total, doc_url.
• mcp_lint_url_invalid_detail_returns_jsonrpc_error — -32602 error code and serde message for unknown variant.
• Schema assertion in mcp_initialize_and_tools_list — $defs.LintUrlDetail.oneOf exposes exactly ["compact", "full"].

Three new unit tests in lib.rs's #[cfg(test)] block covering build_full_lint_payload (happy path + cap rejection) and build_lint_url_result (cap rejection in Full mode).

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5. Documentation — PASS

LintUrlDetail and its variants are doc-commented. LintUrlArgs::detail is doc-commented. CHANGELOG.md updated. docs/src/mcp.md updated with the new detail argument and the 50 KB cap. No public items are undocumented.

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Punch list (warnings, no blockers)

crates/plumb-mcp/src/lib.rs:391–403 — WARNING: unnecessary serialize→parse round-trip.
build_full_lint_payload calls full_json(violations) to get a pretty-printed String, checks byte length, then calls serde_json::from_str(&payload) to convert back to a Value. Functionally correct, but this double-parse is forced by plumb_format::json's string-only API. Not a blocker, but if plumb_format::json ever grows a -> Value variant, this is the first refactor target.

crates/plumb-mcp/src/lib.rs:380 — WARNING: mcp_compact always called in Full mode.
build_lint_url_result always calls mcp_compact(violations), gets (text, compact_structured), and then discards compact_structured when detail == Full. The text is legitimately needed for the shared text block in both modes, so the call itself is correct. The wasted allocation of compact_structured is minor; flagging so it's a known tradeoff rather than an oversight.

crates/plumb-mcp/src/lib.rs:409 — NIT: &'static str overly restrictive.
enforce_response_cap(…, error_message: &'static str) could be &str with no functional impact; it's a private function with one call site. Stack as a nit; doesn't matter in practice.

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Verdict: APPROVE