[tmm]

Decision 3, Rust half: JS's inspector, query metrics, and slowMaterializeThreshold in zero-client, lined up with the Swift port (#210). zero-rust minor changeset, so it rides with 0.2.0.

Swift's half merged as #210; this adds the Rust port, the shared JS vectors, and Swift's replay of them.

let opts = ZeroOptions { slow_materialize_threshold_ms: 5_000.0, ..Default::default() }; // JS default
let insp = zero.inspector();
insp.metrics();                      // client TDigests merged with the server's
insp.client().queries();             // ZQL, row counts, hydrate/update timings
insp.clients_with_queries();
insp.server_version();
insp.analyze_query(&ISSUE_LIST_V2.with(args), AnalyzeQueryOptions { join_plans: Some(true), ..Default::default() });
insp.authenticate("password");

Rust (feat(zero-rust) commit)

• client::{Inspector, InspectorClient, InspectorClientGroup, InspectorQuery, Metrics, AnalyzeQueryOptions, AnalyzeQueryResult, PlanDebugEvent}, tdigest::TDigest, ast::ast_to_zql. Calls return Deferreds.
• Metrics are recorded where JS calls addMetric. A MeasurePush operator times 1 push in 32, weighted 32 (UPDATE_SAMPLE_RATE); reconciles that reach a view aren't timed, as in JS. Evicted queries are kept once an inspector exists. debugPerf is sent at the debug log level.
• Differences from JS, the same as Swift's and documented in PARITY.md's new "The inspector" section:
  • There's no password dialog. A refused request fails until authenticate(password) is called, and an accepted password is presented again after a reconnect.
  • Pending requests fail on a dropped connection or close() instead of hanging.
  • The slow-materialization log is one line.
• Default build: still no third-party dependencies.

Vectors (JS-generated)

• tdigest.json (72), ast-to-zql.json (101), and client-inspector.json (12 scenarios).
• harness.ts gains inspect steps, the inspector and logs observations, and the slowMaterializeThreshold and logLevel options. The logs observation adds expected warnings to client-harden-mutations.json and harden-queries.json.

Swift (test(zero-swift) commit)

• Swift's runner replays all of the above.
• The vectors found three Swift divergences, fixed in feat(zero-swift): inspector, query metrics, and slowMaterializeThreshold #210's second commit: TDigest.quantile trapped instead of returning NaN, debugPerf was missing, and inactivatedAt kept its fraction.
• Swift checks ast-to-zql's unredacted code only, since it has no redactLiterals.

Checked locally

• Rust: cargo clippy --workspace --all-targets --all-features -D warnings, cargo test --workspace --all-features, and cargo doc -D warnings.
• Conformance: 66,370 cases, 0 failures, with the same 2,255 documented exceptions as before. The new files pass 101/101, 72/72, and 12/12 on memory and SQLite.
• Swift: swift format lint --strict, and ConformanceTests with 67 tests passing, client-inspector 12/12 on memory and SQLite.
• JS: pnpm --filter zero-conformance run test passes 265, and the vectors are unchanged afterwards.
• Benchmarks, base vs branch alternating: materialize, put, and optimistic update are within ±7% in both directions. Round trip first read +17%/+19%; 6 more alternating rounds put it at +1.6%/+3.7%/+2.2% with overlapping ranges, which is noise.