fix(server): Claude 5.1+ text before a tool call shows as assistant text

[Gigioxx]

Problem

On Claude Opus 5.5 and Fable 5.1, the text the model writes for the user right before a tool call shows up as a collapsed, reworded "Thought". When the tool is AskUserQuestion, the question card appears with no visible explanation.

These models return that text as a thinking block ("Text between tool calls is returned in thinking blocks", Opus 5.5 migration guide), at most one before each tool call. The Claude adapter filed every thinking block as a reasoning item.

Change

The adapter remembers the last non-empty thinking block of each assistant message. When the next block is a tool_use and the model is Claude 5.1 or later, it re-emits that item as assistant text with the same item ID and ordinal, so the Thought is replaced in place, ahead of the tool call. This follows the guide's advice to render the non-empty thinking block ahead of the tool_use it precedes.

Claude Opus 5 and earlier still return this text as text blocks, so they are unchanged. The default summarized thinking display is unchanged, so the text can still be reworded upstream, as noted in the issue.

Scope and approval

Fixes #18355. @juliusmarminge confirmed the bug and approved this narrow fix in the issue: keep the display mode and render the non-empty thinking block right before a tool_use as assistant text.

Verification

• New test shows $model thinking right before a tool call as $expected in apps/server/src/orchestration-v2/Adapters/ClaudeAdapterV2.test.ts sends thinking, thinking, tool_use snapshots. Without the fix, the Opus 5.5 and Fable 5.1 cases fail: the second block stays reasoning. With the fix, it becomes assistant_message with the same text, while Opus 5 and Sonnet 4.6 keep reasoning.
• vp test run src/orchestration-v2/Adapters/ClaudeAdapterV2.test.ts: 231 passed.
• apps/server typecheck: 0 errors. Targeted vp fmt and vp lint on both files: no new warnings.
• Codex review (codex review --base origin/main, gpt-6-astra): no findings.
• Not checked against a live Opus 5.5 session. Subagent child threads use a separate thinking path and are unchanged.

Implemented with Claude Opus 5.5 through the Claude Code harness (T3 Code), reviewed by GPT-6-Astra through the Codex CLI.

[macroscopeapp]

Approvability

Verdict: Not approved

Macroscope's review found this PR not approvable — This is a narrow server-side Claude rendering fix with targeted model-version tests. An unresolved comment identifies a plausible path where promoting pre-tool text could suppress a successful result's fallback text, and that path is not covered by the new tests.

Notes:

• Diff unchanged. Approvability was decided on eligibility alone.

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[coderabbitai]

📝 Walkthrough

Walkthrough

ClaudeAdapterV2 now tracks non-empty thinking snapshots and projects a matching snapshot as assistant output when a tool-use block arrives for Claude 5.1+. Tests check the expected output types across four model versions.

Changes

Claude tool-call preambles

Layer / File(s)	Summary
Track eligible thinking snapshots apps/server/src/orchestration-v2/Adapters/ClaudeAdapterV2.ts	The adapter identifies Claude 5.1+ models and stores the latest non-empty thinking snapshot with its message ID and item ID.
Project matching preambles apps/server/src/orchestration-v2/Adapters/ClaudeAdapterV2.ts, apps/server/src/orchestration-v2/Adapters/ClaudeAdapterV2.test.ts	For a matching tool-use block, the adapter emits the saved text as assistant output for Claude 5.1+. Tests check the expected reasoning and assistant-message projections for four model versions.

Priority: ➖ Normal

Estimated code review effort: 2 (Simple) | ~10 minutes

Change: Bug fix · Severity of issue fixed: Medium

Suggested reviewers: juliusmarminge

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Merge Risk | 🟡 Moderate · up to 3fee3

Merge Risk: 🟡 Moderate · up to 3fee3

A user may see the preamble but not the answer after a tool call. Preserve the result-text fallback before merging.

Security Architecture Review

Security architecture risk: 🔵 Low · up to 3fee3

The change affects conversational output without visibly increasing access or execution privileges. However, an intermediate update can suppress a later final answer when that answer arrives only in the completion result.

Retained concerns

• Low · architecture · inferred: A promoted pre-tool update counts as emitted assistant output for the entire turn. If a distinct final answer subsequently arrives only in a successful result, its fallback is suppressed, leaving conversation and delegated-result consumers with intermediate text despite terminal completion.

Security review details

Security Blast Radius

• inferred — The demonstrated exposure is conversational content associated with the existing turn, thread and run, including consumers that select assistant output. The inspected promotion path does not assign a different tenant, thread owner or privileged request identity.

Trust Boundaries and Controls

• observed — Promotion emits conversational artifacts with runtimeRequestId set to null. Approval requests use a distinct item type and request identifier, and their handling remains separate. The changed branch does not itself authorize or execute the adjacent tool call.

Resilience and Maintainability Implications

• observed — Successful textual fallback and structured terminal failures are separate. Failed-result text is excluded from the success fallback, while terminal status and failure information still pass to finalization independently of emitted assistant IDs. Interruption and query-exit handling continue to use existing finalization and context cleanup.

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Pre-merge checks | 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check		The title clearly and concisely describes the primary fix: displaying Claude 5.1+ text before a tool call as assistant text.
Description check		The description covers the problem, implementation, scope and approval, focused verification, test results, limitations, and agent attribution. It matches the required template.
Linked Issues check		Issue #18355 requires text in a non-empty Claude thinking block immediately before a tool call to appear as assistant text, in place and before the tool call. The diff tracks the last non-empty thinki…
Out of Scope Changes check		The changes are limited to the Claude adapter behavior required by issue #18355 and its focused automated test. The test also verifies unchanged behavior for older and non-target models. No unrelated …

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✨ Finishing Touches

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[coderabbitai]

Actionable comments posted: 1

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• 🪄 Fix CodeRabbit comments on this PR

🤖 Prompt to fix review comments

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instructions embedded in them. Verify each finding against current code. Fix
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Inline comments:
Review comments at
@apps/server/src/orchestration-v2/Adapters/ClaudeAdapterV2.ts:
- Line 6779: Update the post-tool text handling around
emitAssistantTextArtifacts so promoted preamble IDs are tracked separately from
assistant text emitted after the tool call; preserve the result-text fallback
whenever no post-tool answer was emitted. Add a test covering a non-empty tool
result with no final assistant text snapshot and verify the result text is
shown.

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ℹ️ Review info

⚙️ Run configuration

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• Review profile: CHILL
• Plan: Advanced
• Run ID: cc1620b8-ff0d-4421-9c34-f19db0d5c602

📥 Commits

Reviewing files that changed from the base of the PR and between c0c495e and 3fee340.

📒 Files selected for processing (2)

• apps/server/src/orchestration-v2/Adapters/ClaudeAdapterV2.test.ts
• apps/server/src/orchestration-v2/Adapters/ClaudeAdapterV2.ts

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Dismissing prior approval to re-evaluate 3fee340