fix(runner): always emit MESSAGES_SNAPSHOT to prevent compaction failures by markturansky · Pull Request #1693 · ambient-code/platform

markturansky · 2026-06-16T00:30:29Z

Summary

C1 — grpc_transport.py: Skip gRPC messages with empty payloads instead of building an empty-content message. An empty-content message causes process_messages to return "", which triggers an early RunFinishedEvent before _stream_claude_sdk ever runs — so run_messages stays empty and MESSAGES_SNAPSHOT is never emitted. Affects both Operator-managed and control-plane-reconciled runner sessions.
C2 — run.py: Assign UUIDs to message dicts missing an id in to_run_agent_input. Without ids, upsert_message falls back to append on every call, creating duplicates in the snapshot for multi-turn sessions going through the gRPC dict message path.
C3 — adapter.py: Remove the if run_messages: guard around MESSAGES_SNAPSHOT emission. Runs that produce no assistant output (interrupted, halted on frontend tool, state-management-tool-only turns) still need a snapshot so compactFinishedRun can succeed. When run_messages is empty the snapshot contains the stamped input history, which is sufficient. Without a snapshot, compaction logs "session corrupted, keeping raw events" and chat history is lost after the tail-read optimization (ffe4a21).

Root cause

compactFinishedRun (backend agui_store.go) requires MESSAGES_SNAPSHOT to be present in the JSONL to perform compaction. If absent, it aborts and leaves raw streaming delta events in the file. On the next large-session tail-read (8e3bac3), those deltas may be missing from the head scan and the user sees blank chat history on reconnect.

The MESSAGES_SNAPSHOT gap was introduced when ambient-control-plane added a second reconciled runner path: control-plane sessions reach the runner via gRPC (GRPCSessionListener) rather than HTTP, and the gRPC path has different message-shape guarantees that exposed all three gaps simultaneously.

Test plan

Operator-managed session: send multiple messages, navigate away and back — chat history intact
Control-plane-reconciled session: same navigation test
Session where Claude calls only state-management tools (no text output): navigate away, verify prior history still present on return
Session interrupted mid-run (stop button): reconnect, verify history from previous complete turns is intact
Check runner logs: MESSAGES_SNAPSHOT log line should appear for every RUN_FINISHED/RUN_ERROR turn
Check backend logs: compaction log should show X raw events → Y snapshot events (not "session corrupted")

🤖 Generated with Claude Code

Summary by CodeRabbit

Release Notes

Bug Fixes
- Improved handling of empty or malformed messages to prevent processing failures
- Enhanced message snapshot construction to be more reliable across scenarios
- Added automatic message ID generation to ensure data consistency
- Strengthened validation for incoming message payloads with better error logging

…ures Three fixes to ensure MESSAGES_SNAPSHOT is always emitted, which is required for compactFinishedRun to succeed. Without it, sessions are marked corrupted and chat history is lost after the JSONL tail-read optimization (ffe4a21). - adapter.py: Remove `if run_messages:` guard around MESSAGES_SNAPSHOT emission. Runs that produce no assistant output (interrupted, halted on frontend tool, state-tool-only) still need a snapshot so compaction can succeed. When run_messages is empty the snapshot is the stamped input history, which is sufficient for compaction to find MESSAGES_SNAPSHOT and atomically replace the JSONL. - grpc_transport.py: Skip empty-payload gRPC messages instead of building a message with empty content. An empty-content message causes process_messages to return "" which triggers an early RunFinishedEvent before _stream_claude_sdk runs, so run_messages stays empty and MESSAGES_SNAPSHOT is never emitted. Affects both Operator-managed and control-plane-reconciled runner sessions. - run.py: Assign UUIDs to message dicts that lack an id in to_run_agent_input. Without ids, upsert_message falls back to append for every message, creating duplicates in the MESSAGES_SNAPSHOT for multi-turn sessions going through the gRPC dict message path. Co-Authored-By: Claude <noreply@anthropic.com>

netlify · 2026-06-16T00:30:34Z

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coderabbitai · 2026-06-16T00:30:42Z

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Reviewing files that changed from the base of the PR and between 7e918dd and 2412f5a.

📒 Files selected for processing (3)

components/runners/ambient-runner/ag_ui_claude_sdk/adapter.py
components/runners/ambient-runner/ambient_runner/bridges/claude/grpc_transport.py
components/runners/ambient-runner/ambient_runner/endpoints/run.py

📝 Walkthrough

Walkthrough

Three defensive fixes in the ambient runner message pipeline: incoming messages are normalized with injected UUIDs when id is missing; the gRPC transport skips empty-payload user events with a warning; and MESSAGES_SNAPSHOT construction is unconditional, gated only on the final combined list being non-empty.

Changes

Ambient Runner Message Pipeline Robustness

Layer / File(s)	Summary
UUID injection for incoming messages `ambient_runner/endpoints/run.py`	`to_run_agent_input()` iterates `self.messages` and injects a UUID `id` into any dict missing one before constructing `RunAgentInput`.
Empty-payload guard in gRPC transport `ambient_runner/bridges/claude/grpc_transport.py`	`_handle_user_message` returns early with a `seq`-keyed warning when `msg.payload` is absent or whitespace-only, preventing an empty `bridge.run()` turn.
Unconditional `MESSAGES_SNAPSHOT` construction `ag_ui_claude_sdk/adapter.py`	Removes the `run_messages`-truthy gate; always builds `enriched`, stamps `input_data.messages` with the run-start timestamp, and skips yield only when `all_messages` is empty.

🚥 Pre-merge checks | ✅ 7 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 66.67% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (7 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title follows Conventional Commits format (fix(runner): ...) and accurately describes the main fix: ensuring MESSAGES_SNAPSHOT is always emitted to prevent compaction failures.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Performance And Algorithmic Complexity	✅ Passed	Three changes analyzed: (1) adapter.py removes conditional guard around MESSAGES_SNAPSHOT emission—adds one O(N) loop at shutdown (N typically <100 msgs, not nested); (2) run.py adds UUID assignmen...
Security And Secret Handling	✅ Passed	No security violations found. Caller token not logged; user_id sanitized before logging; UUIDs generated securely; no hardcoded credentials, SQL/command/path-traversal injection, K8s Secret OwnerRe...
Kubernetes Resource Safety	✅ Passed	PR modifies only Python source code (adapter.py, grpc_transport.py, run.py); contains no Kubernetes manifests or resource definitions. Kubernetes Resource Safety check is not applicable.

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mergify · 2026-06-16T00:52:58Z

Merge Queue Status

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✅ Merged — 2026-06-16 00:53 UTC · at 2412f5ad7cc89c83fc020141c4020c8e4033966b · squash

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mergify Bot merged commit b85feee into main Jun 16, 2026
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fix(runner): always emit MESSAGES_SNAPSHOT to prevent compaction failures#1693

fix(runner): always emit MESSAGES_SNAPSHOT to prevent compaction failures#1693
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fix/messages-snapshot-missing

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