* test(core): strengthen git-memory system prompt stability integration coverage
Switch git-memory HTTP integration tests to OpenAI model handles and add assertions that system prompt content remains stable after normal turns and direct block value updates until explicit recompilation or reset.
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* fix(core): preserve git-memory formatting and enforce lock conflicts
Preserve existing markdown frontmatter formatting on block updates while still ensuring required metadata fields exist, and make post-push git sync propagate memory-repo lock conflicts as 409 responses. Also enable slash-containing core-memory block labels in route params and add regression coverage.
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* fix(memfs): fail closed on memory repo lock contention
Make memfs git commits fail closed when the per-agent Redis lock cannot be acquired, return 409 MEMORY_REPO_BUSY from the memfs files write API, and map that 409 back to core MemoryRepoBusyError so API callers receive consistent busy conflicts.
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* chore(core): minimize git-memory fix scope to memfs lock and frontmatter paths
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* chore: drop unrelated changes and keep memfs-focused scope
Revert branch-only changes that are not required for the memfs lock contention and frontmatter-preservation fix so the PR contains only issue-relevant files.
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* fix(memfs): lock push sync path and improve nested sync diagnostics
Serialize memfs push-to-GCS sync with the same per-agent Redis lock key used by API commits, and add targeted post-push nested-block diagnostics plus a focused nested-label sync regression test for _sync_after_push.
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Co-authored-by: Letta <noreply@letta.com>
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