**Map the environment before changing code.** Silent failures often stem from runtime assumptions—missing paths, wrong user context, or unmet prerequisites. Verify the actual environment first.
**Silent termination is a logging failure.** When a script exits non-zero with no output, the bug is in error handling, not the command. Log at operation entry points, not just on success.
**Pipefail is not a silver bullet.** It propagates exit codes but doesn't guarantee visibility. Pair with explicit error logging for external commands (git, curl, etc.).
**Debug the pattern, not the symptom.** If one HTTP call fails with 403, audit all similar calls. If one script has the same bug, find where it's duplicated.
**Exit codes don't indicate output.** Commands like `grep -c` exit 1 when count is 0 but still output a number. Test both output and exit status independently.
**User context matters at every layer.** When using `gosu`/`su-exec`, ensure all file operations occur under the target user. Create resources with explicit `chown` before dropping privileges.
**Fail fast with actionable diagnostics.** Entrypoints should exit immediately on dependency failures with clear messages explaining *why* and *what to do*.
**Validate semantic types, not just names.** Don't infer resource type from naming conventions. Explicitly resolve whether an identifier is a user, org, or team before constructing URLs.
**403 errors can signal semantic mismatches.** When debugging auth failures, consider whether the request is going to the wrong resource type.
**Auth failures are rarely isolated.** If one endpoint requires credentials, scan for other unauthenticated calls. Environment assumptions about public access commonly break.
**Test against the most restrictive environment first.** If it works on a locked-down instance, it'll work everywhere.
## State & Configuration
**Idempotency requires state awareness.** Distinguish "needs setup" from "already configured." A naive always-rotate approach breaks reproducibility.
**Audit the full dependency chain.** When modifying shared resources, trace all consumers. Embedded tokens create hidden coupling.
**Check validity, not just existence.** Never assume a credential is invalid just because it exists. Verify expiry, permissions, or other validity criteria.
**Conservative defaults become problematic defaults.** Timeouts and limits should reflect real-world expectations, not worst-case scenarios. When in doubt, start aggressive and fail fast.
**Documentation and defaults must stay in sync.** When a default changes, docs should immediately reflect why.
## Validation & Testing
**Add validation after critical operations.** If a migration commits N commits, verify N commits exist afterward. The extra lines are cheaper than debugging incomplete work.
**Integration tests should cover both paths.** Test org and user scenarios, empty inputs, and edge cases explicitly.
**Reproduce with minimal examples.** Running the exact pipeline with test cases that trigger edge conditions catches bugs early.
**Treat "works locally but not in production" as environmental, not code.** The bug is in assumptions about the runtime, not the logic itself.
