[adewale]

What

Capture the repository's Workers runtime/CI lessons, reusable engineering guidance, and a dated cross-project Ruff rollout retrospective.

Why

The repairs in #2 resolved the last rollout blockers, but their operational lessons were spread across PR descriptions and chat history. The retrospective preserves evidence and distinguishes completed merges from incomplete application coverage.

How

• Add LESSONS_LEARNED.md with the actual runtime/configuration/test-harness findings and tested versions.
• Add docs/engineering-guidance.md for reusable diagnosis, validation, toolchain, and merge practices.
• Add a dated retrospective covering all 29 merged rollout PRs: 28 public links and one anonymized private-repository entry, plus CI receipts and explicitly separate follow-ups.
• Link all three documents from the README; host the shared documents here for both Workers repositories.
• Be explicit that LangChain's XPASS is a placeholder and the Workers AI xfail does not start the server.

Validation

• Checked the 29-PR inventory against GitHub; all are merged.
• Validated all 8 relative links in the new documents and README section, plus 28 unique public inventory URLs and one anonymized private-repository entry.
• uv run ruff check . and staged diff whitespace checks pass.
• Full unchanged integration suite and Ruff passed in fresh GitHub CI on the anonymized documentation commit; Semgrep also passed.
• Documentation only: no runtime, dependency, workflow, or application UI changes. Screenshots are not applicable.

Risk

Low. Historical claims link to merged revisions and dated CI runs; limits and floating toolchain layers are explicit. Merge this PR before the companion issues documentation PR, whose new cross-repository links point to these documents on main.