[Bug]: Gemini Model missing thought_signature as being an aggregator in MoA model

[kenmjlee]

Bug Description

When Hermes Agent routes a request through the Gemini provider in MoA (aggregator) mode, the Gemini API rejects every function call with a 400 INVALID_ARGUMENT error stating that thought_signature is missing from functionCall parts. This makes it impossible for any Gemini-based model to act as an aggregator worker but they work independently well as either a reference model or a main model.

Steps to Reproduce

1. Configure Hermes Agent with a Gemini model (e.g., gemini-3.5-flash) as the aggregator provider.
2. Enable MoA mode as the main model
3. Chat with the agent
4. Observe the thought_signature error in the logs after references return results.

Expected Behavior

• Gemini aggregator workers should function normally in MoA mode.

Actual Behavior

Every tool call from a Gemini aggregator results in a 400 INVALID_ARGUMENT error.

Affected Component

CLI (interactive chat)

Messaging Platform (if gateway-related)

N/A (CLI only)

Debug Report

2026-07-15 15:36:37,322 WARNING [20260715_153436_1c53f7] agent.conversation_loop: API call failed (attempt 1/3) error_type=GeminiAPIError thread=Thread-30 (run):281471587447136 provider=moa base_url=moa://local model=testing summary=HTTP 400: Gemini HTTP 400 (INVALID_ARGUMENT): Function call is missing a thought_signature in functionCall parts. This is required for tools to work correctly, and missing thought_signature may lead to degraded model performance. Additional data, function call `default_api:terminal` , position 2. Please refer to https://ai.google.dev/gemini-api/docs/thought-signatures for more details.
2026-07-15 15:36:37,359 ERROR [20260715_153436_1c53f7] agent.conversation_loop: Non-retryable client error: Gemini HTTP 400 (INVALID_ARGUMENT): Function call is missing a thought_signature in functionCall parts. This is required for tools to work correctly, and missing thought_signature may lead to degraded model performance. Additional data, function call `default_api:terminal` , position 2. Please refer to https://ai.google.dev/gemini-api/docs/thought-signatures for more details.

Operating System

macOS 26.5.2 (deploying the latest hermes image via Apple Container)

Python Version

3.13.5

Hermes Version

0.18.2

Additional Logs / Traceback (optional)

Root Cause Analysis (optional)

No response

Proposed Fix (optional)

No response

Are you willing to submit a PR for this?

• I'd like to fix this myself and submit a PR

[GottZ]

Cross-referencing open PRs: 2 open PRs currently address this issue.

• fix(gemini): emit thoughtSignature sentinel for cross-provider/MoA tool calls (#65092) #65294 (+41/-2) — fixes the root cause: the diff emits thoughtSignature on every functionCall part in gemini_native_adapter.py, falling back to Google's documented sentinel skip_thought_signature_validator when extra_content is missing, so the 400 error from the issue log can no longer occur; a new test covers exactly the tool_call-without-signature case (MoA/cross-provider).
• fix(agent): preserve Gemini thought_signature in MoA aggregator mode #66212 (+21/-2) — fixes the root cause: verified against run_agent.py:5898, _sanitize_tool_calls_for_strict_api strips extra_content (thought_signature) when the passed model is not Gemini-family — in MoA, agent.model is the virtual preset name, so the signature was always removed; the diff resolves the real aggregator model at both callsites, preserving the original signature. However, it only helps when the signature is present in the history before sanitization, and it ships no tests.

Suggested consolidation: merge #65294 — it guarantees the presence of thoughtSignature unconditionally, including cases where the signature never reached the history (cross-provider references, serialization, session restore), where #66212 would be ineffective, and it includes a targeted regression test for the signature-less case. #66212 should not be closed as a duplicate but treated as a complementary quality improvement: it preserves the real thought_signature instead of the sentinel (less degradation per Gemini docs), but should add tests for both callsites and be rebased on #65294 before merge. Still open: verification in a live MoA setup that the sentinel variant is durably accepted by the Gemini API in aggregator chains.

Cross-PR triage: each diff was read against this issue; verdicts reflect diff content, not PR titles. Human-reviewed before posting.