docs(release-process): add post-fix repro verification policy

Closes M12

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

docs/reference/release-process.md

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+# Release Process Reference
+
+This reference captures release gates that are easy to miss during urgent fixes.
+
+## Post-Fix Repro Verification
+
+For race-condition and concurrency fixes, CI green is necessary but not
+sufficient.
+
+Before closing the source issue, the original issue reporter must re-run the
+documented reproducer against the fix commit. If the reporter is unavailable, a
+maintainer must run the same reproducer in an equivalent environment.
+
+This policy applies to bugs involving:
+
+- duplicate streaming output
+- repeated internal prompt injection
+- session recovery races
+- background task wake races
+- runtime fallback retry races
+- team mailbox delivery races
+- test contamination caused by shared mocks or module state
+
+### Required checklist
+
+- Record the issue number and fix commit hash.
+- Confirm the reproducer is documented in the issue or PR.
+- Build or install the exact fix commit under test.
+- Run the reproducer without local patches.
+- Capture the command, input prompt, config, provider, model, and platform.
+- Confirm the original failure is absent.
+- Confirm no new adjacent failure appears in logs or terminal output.
+- Link the successful repro result before closing the issue.
+
+### Reporter path
+
+1. Ask the original reporter to test the fix commit.
+2. Provide exact install or checkout instructions.
+3. Ask for terminal output, logs, or a short screen recording when relevant.
+4. Close the issue only after the reporter confirms the failure no longer
+   reproduces.
+
+### Maintainer fallback path
+
+Use this path when the reporter is unavailable or cannot test the fix.
+
+1. Recreate the reported environment as closely as practical.
+2. Use the same provider and model class if provider behavior is part of the
+   failure.
+3. Run the documented reproducer against the fix commit.
+4. Attach the maintainer repro notes to the issue.
+5. State which parts of the environment could not be matched.
+
+### Environmental escalation path
+
+If the reproducer depends on unavailable local state, credentials, provider
+behavior, timing, or platform details:
+
+1. Keep the issue open.
+2. Label or note it as environment-dependent repro pending.
+3. Ask for the missing environment details or sanitized logs.
+4. Add a maintainer-owned minimized reproducer if one can be derived.
+5. Land extra diagnostics when the failure cannot be observed directly.
+6. Re-run the repro after diagnostics or environment access is available.
+
+Do not close a race-condition issue based only on unit tests, typecheck, or a
+green CI run.
+
+### Closure note template
+
+```text
+Post-fix repro verification:
+- Issue: #<number>
+- Fix commit: <hash>
+- Verified by: <reporter or maintainer>
+- Environment: <os, runtime, provider, model>
+- Reproducer: <link or summary>
+- Result: original failure no longer reproduces
+```