test: guard cost report agent coverage

[moose-lab]

Audit conclusion

• Issue perf: Cost & Usage 页在大量历史会话下会卡死 — 成本报表扫描未走增量缓存 #49 is not a signal to add cost/usage scanners for every Local CLI agent.
• The current Cost & Usage report has two real providers: Claude Code via ~/.claude/projects and Codex via ~/.codex/sessions / archived sessions.
• Claude already uses the IM-23 (path, mtimeMs, size) discovery cache; Codex now uses scanCodexSessionCached() from perf: cache Codex cost session scans #56.
• Other Local CLI agents are launch/runtime choices, but DevLog does not currently parse a durable local cost/usage history source for them. Adding fake scanners would broaden scope without data.

Summary

• add explicit Cost Report provider and Local CLI agent coverage metadata
• mark Claude and Codex as supported with their historical source path and cache strategy
• mark the remaining Local CLI agents as intentionally unsupported for Cost Report until a durable usage source is implemented
• add guardrail tests so future agents/providers cannot be added without updating cost coverage

Verification

• TZ=Asia/Shanghai node --test --import tsx --test-reporter spec src/core/tests/cost-tracker.test.ts
• git diff --check
• bun run typecheck
• TZ=Asia/Shanghai bun run test
• pre-commit quality gate: git diff --cached --check && bun run typecheck && TZ=Asia/Shanghai bun run test

[claude]

Claude finished @moose-lab's task in 1m 40s —— View job

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PR Review

• Gather context
• Read changed files
• Review diff
• Post findings

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Findings

• [should-fix] cost-tracker.test.ts:98-102 — .filter((coverage) => coverage.supported) has no type predicate, so TypeScript does not narrow the union before .map((coverage) => coverage.provider). property only exists on the supported: true branch; accessing it on the bare union type is a type error. Fix: .filter((coverage): coverage is Extract<CostReportAgentCoverage, { supported: true }> => coverage.supported). If this compiles today it is likely because __tests__ files are excluded from tsconfig.json — but the latent unsoundness is worth closing.

• [nit] cost-tracker.ts:26-71 — The key type of COST_REPORT_AGENT_COVERAGE is inferred as string. Typing it as Record<(typeof LOCAL_CLI_AGENT_DEFINITIONS)[number]['id'], CostReportAgentCoverage> would give compile-time enforcement (not just test-time) that every agent ID is covered. The test guardrail already handles this at runtime, so not a blocker.

• [nit] cost-tracker.ts:31,37 — The cacheStrategy strings are long prose. They document intent well, but there is no machine-readable enum distinguishing "mtime cache", "incremental", etc. If the strings are ever queried programmatically (e.g., for a UI badge), a structured field would be better. No action needed now.

Verdict: APPROVE

The overall design is sound: deriving CostProvider from the as const array, using a discriminated union for coverage, and the three guardrail tests together enforce that the coverage map stays in sync with LOCAL_CLI_AGENT_DEFINITIONS and that COST_REPORT_PROVIDERS matches what is actually supported. The only issue worth addressing before merge is the missing type predicate in the third test.