[G3] Harness expansion through relayhistory: Cursor and Grok in burn (SourceKind, pricing, TOOL_ALIASES, overhead mapping, fidelity policy) and collector-backlog transfer

[willwashburn]

Part of #553 (group 3 — depends on burn #562 cutover (default backend = relayhistory) and relayhistory #166 Cursor / #167 Grok parity; parallel with #563).

Problem

burn's SourceKind (crates/relayburn-sdk/src/reader/types.rs:32-55) is claude-code | codex | opencode | anthropic-api | openai-api | gemini-api; only the first three are produced. With relayhistory as the source, Cursor and Grok sessions arrive for free, and every burn per-harness table needs an entry. burn #489 (Grok) planned an 11-PR stack; after cutover only the burn-side slices of it remain.

Scope

1. Types: SourceKind::{Cursor, Grok} ("cursor", "grok"), RelationshipSourceKind variants, Harness variants, PendingStampHarness::{Cursor, Grok} (+ packages/sdk-node/src/index.d.ts unions), AdapterName for gap warnings. Decide whether SourceKind becomes an open string mirroring relayhistory's Source to avoid a burn release per new collector — recommend keeping the enum for exhaustiveness in pricing/overhead tables but adding SourceKind::Other(String) that is priced/classified with defaults and reported as FidelityClass::Partial.
2. Classifier: TOOL_ALIASES (reader/classifier.rs:54-78) entries for Cursor tools (read_file, edit_file, run_terminal_cmd, codebase_search, grep, …) and Grok tools (Shell→Bash, StrReplace→Edit, CallMcpTool→Mcp, WebSearch/WebFetch→WebFetch, per Add Grok CLI harness support #489's table).
3. Pricing: xAI entries (grok-composer-2.5-fast, grok-build, $1/$2 per 1M per Add Grok CLI harness support #489) in crates/relayburn-sdk/data/models.dev.json via pnpm run pricing:update + overrides; Cursor model ids observed in relayhistory's Cursor fixture.
4. Fidelity policy (reader/fidelity.rs): per-source coverage builders from relayhistory SourceCapabilities + NormalizedUsage.accounting: Grok = UsageGranularity::PerSessionAggregate/Partial with the ContextProxy accounting (relayhistory records context_total_tokens only; burn's estimator from Add Grok CLI harness support #489 — bytes/4 output, context-delta input — lives in analyze/, not in the reader, and is applied only when accounting == ContextProxy); Cursor = whatever relayhistory reports (full if usage present).
5. Overhead (analyze/overhead.rs:73-89 source→file mapping): Grok → AGENTS.md (+ prompt_context.json path from relayhistory session metadata), Cursor → .cursor/rules / AGENTS.md as characterized.
6. Subagent tree / relationships: consume relayhistory's grok_subagent_dir and Cursor relationships through the [G2] RelayHistoryBackend: depend on the ai-hist crate, map SessionEvidence onto burn's record types behind the backend seam (feature-flagged, off by default) #557 adapter (no per-harness code).
7. Collector backlog: comment on burn Collector: Gemini CLI #13–Collector: Cortex Code (Snowflake) #36, Octofriend SQLite fallback collector for Synthetic-routed traffic #98, Add Grok CLI harness support #489 that sourcing moved to relayhistory (link the mirrored issue from relayhistory Claim at most one pending stamp per session (#162) #177) and that burn's remaining work per collector is items 2–5 above; close them not_planned once the mirrors exist. Update the collector label description.
8. README.md harness list, CHANGELOG.md.

Acceptance

• burn summary --by-provider on a relayhistory store containing the Cursor and Grok corpus fixtures shows xai/Cursor rows with priced cost and a fidelity note for Grok.
• burn hotspots --group-by bash-verb attributes Grok Shell and Cursor run_terminal_cmd calls.
• burn overhead --kind agents-md includes a Grok session.
• Smoke test (crates/relayburn-cli/tests/smoke.rs) harness-name expectations updated; cargo test --workspace green.

Out of scope

Any log parsing in burn.