fix(review): add retry logic and Pass 1 validation for 99.9% success rate

[factory-nizar]

Summary

Code review success rate is currently 96% (per Metabase dashboard 232). Target is 99.9%.

Data analysis shows failures are concentrated in the Pass 1 to Pass 2 transition for CI reviews: ~476 out of 24,484 eligible reviews fail at Pass 2 over 30 days. Pass 1 has a 100% completion rate among eligible reviews.

Linear: AUT-1100

Root Causes

1. No retry on Droid Exec failures - transient model/API errors immediately kill the run
2. No retry on MCP server registration - a single registration failure kills the entire action
3. No retry on gh pr checkout - transient git/GitHub API failures kill the run
4. No retry on gh pr diff fallback - transient failures in diff computation
5. No validation of Pass 1 candidates JSON before Pass 2 - malformed/missing candidates cause Pass 2 to fail with no graceful degradation

Changes

base-action/src/run-droid.ts

• Add retry (3 attempts, exponential backoff 5s/10s/30s) around Droid Exec spawn+wait loop
• Add retry (3 attempts, 2s initial delay) around individual MCP server droid mcp add registrations
• Inline retryWithBackoff helper (base-action is a separate package)

src/tag/commands/review.ts and src/entrypoints/generate-review-prompt.ts

• Wrap gh pr checkout in retryWithBackoff (3 attempts, 3s delay)

src/github/data/review-artifacts.ts

• Wrap gh pr diff fallback in retryWithBackoff (3 attempts, 3s delay)

src/entrypoints/prepare-validator.ts and action.yml

• Validate Pass 1 candidates JSON exists and has valid schema (comments array) before running Pass 2
• If invalid, skip Pass 2 gracefully (set validator_should_run=false) instead of failing the entire pipeline
• Updated action.yml condition to check validator_should_run output

src/entrypoints/gitlab-prepare-validator.ts

• Same Pass 1 candidates validation for the GitLab flow

base-action/test/run-droid-mcp.test.ts

• Update MCP failure test timeout to account for retry backoff delays

Test Results

• All 451 tests pass
• TypeScript typecheck passes (both root and base-action)
• Prettier formatting verified

Expected Impact

With these changes, the ~4% failure rate should drop significantly:

• Transient model/API failures (the largest category) will retry up to 3 times
• MCP registration failures will retry up to 3 times
• Git checkout/diff failures will retry up to 3 times
• Pass 1 JSON validation failures will degrade gracefully (skip Pass 2) rather than failing the whole pipeline

[factory-droid]

Droid encountered an error —— View job

---

Droid is reviewing code and running a security check…

[factory-nizar]

Withdrawn — addressing directly in the PR.

[wenemily]

trust