perf: coalesce slack user info lookups

[seven332]

Summary

• add a request-local Slack user info resolver with successful-result caching and in-flight lookup coalescing
• share the resolver between Slack message enrichment and conversation context building
• add bounded resolver telemetry and route coverage for duplicate lookup reuse plus partial user-info failure

Closes #20718

Verification

• pnpm -F api exec vitest run src/signals/routes/tests/test-telegram-state.test.ts
• pnpm -F api exec vitest run src/signals/routes/tests/test-slack-dispatch-probe.test.ts
• pnpm -F api exec vitest run src/signals/routes/tests/integrations.bdd.test.ts
• pnpm -F api check-types
• pnpm -F api lint

Note

• Local pre-commit full knip is currently blocked by unrelated existing platform unused exports outside this PR. The related unused exported type introduced during this change was fixed before commit.

[codecov]

Codecov Report

❌ Patch coverage is 89.85507% with 7 lines in your changes missing coverage. Please review.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
...rc/signals/services/zero-slack-webhooks.service.ts	72.22%	5 Missing ⚠️
...s/api/src/signals/external/slack-message-client.ts	95.83%	2 Missing ⚠️

📢 Thoughts on this report? Let us know!

[github-actions]

API preview: https://pr-20724-api.vm6.ai

[seven332]

Code Review: PR #20724

Summary

Reviewed the Slack user info resolver changes, route coverage, telemetry dimensions, and async cleanup behavior. I did not find blocking logic, performance, security, testing, or deployment-compatibility issues.

Key Findings

Critical Issues (P0)

• None found.

High Priority (P1)

• None found.

Testing Review

Coverage

• perf: coalesce duplicate Slack users.info lookups between message enrichment and conversation context building -> covered by turbo/apps/api/src/signals/routes/__tests__/test-telegram-state.test.ts.
• partial Slack users.info failure remains non-fatal -> covered by turbo/apps/api/src/signals/routes/__tests__/test-telegram-state.test.ts.
• resolver timing action and privacy of telemetry dimensions -> covered by turbo/apps/api/src/signals/routes/__tests__/integrations.bdd.test.ts and turbo/apps/api/src/signals/routes/__tests__/test-telegram-state.test.ts.

Convention Compliance

• No internal vi.mock() usage or direct fetch mocking found in the PR diff.
• No fake timers, fixed sleeps, timeout increases, filesystem mocks, DB mocks, or lint/type suppressions found.
• Tests exercise the API route path and centralized Slack boundary mocks instead of importing/testing the resolver directly.

Testing Verdict: Adequate

Bad Smell Analysis

• Mock violations: 0
• Test coverage issues: 0
• Defensive programming issues: 0
• Dynamic imports: 0
• Type safety issues in PR diff: 0
• Timer/artificial delay issues: 0
• Deployment compatibility issues: 0

Verification

• pnpm -F api exec vitest run src/signals/routes/__tests__/test-telegram-state.test.ts src/signals/routes/__tests__/test-slack-dispatch-probe.test.ts src/signals/routes/__tests__/integrations.bdd.test.ts passed locally.
• pnpm -F api lint passed locally.
• pnpm -F api check-types was inconclusive locally because this workspace has stale ignored generated connector files under turbo/packages/connectors/src/firewall-metadata/ that are not part of this PR diff. CI lint-types and lint-types-apps are passing on the PR.

Recommendations

• No changes requested.

Verdict

LGTM

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Full review details: codereviews/20260708/pr-20724-*
Testing standards: docs/testing.md