fix(opencode): ensure tool-call/tool-result pairing after normalizeMessages by bvironn · Pull Request #22001 · anomalyco/opencode · GitHub

Issue for this PR

Type of change

Bug fix
New feature
Refactor / code improvement
Documentation

What does this PR do?

Adds ensureToolIntegrity() in the provider transform pipeline, running after normalizeMessages for Anthropic/Bedrock/Vertex-Anthropic. It detects orphaned tool-call parts (no matching tool-result) and injects synthetic error results to keep the session alive.

Why here? normalizeMessages can drop messages with empty content, breaking tool-call/tool-result pairs. By the time the request leaves ProviderTransform.message(), orphaned tool-calls cause a permanent 400 from Anthropic — the corrupted history replays from SQLite on every retry, making the session unrecoverable.

The function is a no-op when pairs are intact (single pass, Map+Set lookups, zero allocation on happy path). It catches corruption from 6 independent vectors in the pipeline — normalizeMessages filtering (V1), error-skip logic in toModelMessages (V2), lost step boundaries during retry (V3), tool-error race conditions (V4), filterCompacted cutting pairs (V5), and the AI SDK producing empty assistant messages (V6). Full analysis in #21326 comment.

How did you verify your code works?

130 existing transform tests pass (one updated for new pipeline ordering)
8 new unit tests: matched pairs (no-op), single/multiple orphans, partial orphans appended to existing tool messages, empty input, string content, full end-to-end through ProviderTransform.message()
bun typecheck clean
Manual reproduction: corrupted a session simulating V1+V5, confirmed the fix prevents the 400

Checklist

I have tested my changes locally
I have not included unrelated changes in this PR

The following comment was made by an LLM, it may be inaccurate:

Great! I found several related PRs. Let me identify the most relevant ones:

Related PRs Found

PR fix(provider): skip empty-text filtering for assistant messages in normalizeMessages (#16748) #16750 - fix(provider): skip empty-text filtering for assistant messages in normalizeMessages (#16748)
- Related: Directly addresses empty-text filtering in normalizeMessages, which is the root cause issue being fixed in PR fix(opencode): ensure tool-call/tool-result pairing after normalizeMessages #22001
PR fix(session): fix root causes and reconstruction of tool_use/tool_result mismatch (#16749) #16751 - fix(session): fix root causes and reconstruction of tool_use/tool_result mismatch (#16749)
- Related: Addresses tool_use/tool_result mismatches, which is the exact problem that PR fix(opencode): ensure tool-call/tool-result pairing after normalizeMessages #22001 aims to prevent with the ensureToolIntegrity function
PR fix: treat "other" as a continue stop reason #20467 - fix: blank assistant text - finish-reason regression after AI SDK v6 migration
- Related: Deals with blank assistant text issues that can break message pairing logic
PR fix: prevent Kimi session poisoning from empty MCP tool-result text #14174 - fix: prevent Kimi session poisoning from empty MCP tool-result text
- Related: Addresses session corruption from empty tool-result text, similar problem domain
PR fix: handle dangling tool_use blocks for LiteLLM proxy compatibility #8497 - fix: handle dangling tool_use blocks for LiteLLM proxy compatibility
- Related: Handles orphaned tool_use blocks without matching results

These are not exact duplicates of PR #22001, but they address related problems in the tool-call/tool-result pairing system. PR #22001 appears to be a comprehensive fix that consolidates lessons from these previous issues.

Thanks for updating your PR! It now meets our contributing guidelines. 👍

Pull request overview

This PR adds a post-normalization safety check to prevent Anthropic-style tool-call history corruption by ensuring every tool-call has a corresponding tool-result, even when upstream transforms drop/alter messages.

Changes:

Added ProviderTransform.ensureToolIntegrity() to detect orphaned tool-calls and inject synthetic error tool-results.
Wired ensureToolIntegrity() into ProviderTransform.message() after normalizeMessages() for Anthropic/Bedrock SDKs.
Expanded/updated provider transform tests to cover multiple orphan scenarios and the full normalize→repair pipeline.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
packages/opencode/src/provider/transform.ts	Introduces ensureToolIntegrity() and applies it after normalizeMessages() for specific providers.
packages/opencode/test/provider/transform.test.ts	Updates an existing Anthropic normalization test expectation and adds a new test suite covering integrity repair cases.

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The tool integrity repair is only enabled for models using @ai-sdk/anthropic and @ai-sdk/amazon-bedrock. This omits the Vertex Anthropic provider (@ai-sdk/google-vertex/anthropic / providerID google-vertex-anthropic), which is treated as Anthropic elsewhere in this module and likely has the same tool-call/tool-result pairing requirement. Consider including that provider in the condition so Vertex Anthropic sessions can’t be corrupted the same way.

Suggested change

      
                if (model.api.npm === "@ai-sdk/anthropic" || model.api.npm === "@ai-sdk/amazon-bedrock") {
          
                if (
          
                  model.api.npm === "@ai-sdk/anthropic" ||
          
                  model.api.npm === "@ai-sdk/amazon-bedrock" ||
          
                  model.providerID === "google-vertex-anthropic"
          
                ) {

Already covered — the condition at line 332 includes model.providerID === "google-vertex-anthropic" alongside the npm checks for @ai-sdk/anthropic and @ai-sdk/amazon-bedrock. This matches the same triple-check pattern used by applyCaching below (lines 336-347).

The npm package for Vertex Anthropic is @ai-sdk/google-vertex/anthropic (a subpath export), so checking model.api.npm alone would miss it — that's why the providerID fallback is there.

…ssages

CI Note: E2E timeouts are unrelated to this change

Both e2e (linux) and e2e (windows) failed with runner timeouts (31m / 33m exceeding the 30-minute limit). Unit tests pass on both platforms.

This PR only modifies the message transform pipeline (transform.ts) — it doesn't touch session lifecycle, TUI rendering, or any code path exercised by the Playwright E2E suite. The function itself is a no-op when tool-call/tool-result pairs are already matched (which they are in normal operation).

Happy to re-trigger if needed, but this appears to be a runner infrastructure issue rather than a regression.

Here's a corrupted session: https://gist.github.com/bvironn/b513c1eafae54291890355ddc7fd1941

Claude Opus 4.6, no interruption — the corruption happens on its own during normal tool execution. The agent made 5 tool calls across 2 steps (mem_search, glob, read), all completed successfully, but 2 tool_results were missing from the ModelMessage[] by the time the next request was sent.

messages.3: `tool_use` ids were found without `tool_result` blocks immediately after:
toolu_01APxrADs7VozN8uWzw9WwHr, toolu_01N8mDEzG8DSTs7UPHFtmgCT

Additional reproduction — real session bricked (April 12, 2026)

Hit this bug again in a live session on WSL2/Ubuntu 24.04 (OpenCode on dev, Anthropic Claude Opus 4.6).

Sequence that triggered it

Session running normally — sdd-init, then web research via webfetch, then checking WSLg via parallel bash calls
Assistant made a todowrite call (internal tool, not MCP) → completed successfully
Assistant generated text after the tool result
Step finished with "finish": "tool-calls" — model wanted to continue
Next API call → 400: tool_use ids found without tool_result blocks
Session permanently bricked

Key evidence from the SQLite session dump

Orphaned tool call: toolu_01U3gvtjXYHzq121oQG6624z (a todowrite)

The part data shows "status":"completed" with valid output — the tool executed fine. But when the message history was serialized for the next API request, the tool_result was not placed in the required user message after the assistant message containing the tool_use.

Error response (from msg_d832e2af7001):

messages.17: `tool_use` ids were found without `tool_result` blocks
immediately after: toolu_01U3gvtjXYHzq121oQG6624z

Why this rules out network/MCP

DNS was verified working (immutable /etc/resolv.conf with Cloudflare) — repo was cloned successfully right before this session
The failing tool is todowrite — an internal OpenCode tool, not an MCP server tool
All previous tool calls in the same session completed normally

Why ensureToolIntegrity() would have caught this

The fix in this PR scans for orphaned tool_use blocks and injects synthetic tool_result messages. This exact scenario — a completed todowrite whose result was lost during serialization — would have been patched before the API call.

Full session data (messages + parts) available on request.

Follow-up: after the error, I did Ctrl+X+U (undo) which removed the failed message from the history, then resent the same prompt — it worked normally. So the session is recoverable via undo, but only if the user knows to do it. ensureToolIntegrity() would make this transparent — no manual intervention needed.

fixed elsewhere thanks for pr

Copilot AI review requested due to automatic review settings April 11, 2026 06:24

github-actions Bot added the needs:compliance This means the issue will auto-close after 2 hours. label Apr 11, 2026

Copilot started reviewing on behalf of bvironn April 11, 2026 06:25 View session

github-actions Bot removed the needs:compliance This means the issue will auto-close after 2 hours. label Apr 11, 2026

Copilot AI reviewed Apr 11, 2026

View reviewed changes

fix(opencode): ensure tool-call/tool-result pairing after normalizeMe…

8521eb6

…ssages

chan1103 mentioned this pull request Apr 14, 2026

fix: Opus prefill rejection during tool-call loops with thinking enabled #22404

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rekram1-node closed this Apr 16, 2026

                 export function message(msgs: ModelMessage[], model: Provider.Model, options: Record<string, unknown>) {
                   msgs = unsupportedParts(msgs, model)
                   msgs = normalizeMessages(msgs, model, options)
+                  if (model.api.npm === "@ai-sdk/anthropic" || model.api.npm === "@ai-sdk/amazon-bedrock") {

fix(opencode): ensure tool-call/tool-result pairing after normalizeMessages by bvironn · Pull Request #22001 · anomalyco/opencode · GitHub

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fix(opencode): ensure tool-call/tool-result pairing after normalizeMessages - #22001

fix(opencode): ensure tool-call/tool-result pairing after normalizeMessages#22001
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fix(opencode): ensure tool-call/tool-result pairing after normalizeMessages by bvironn · Pull Request #22001 · anomalyco/opencode · GitHub

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bvironn commented Apr 11, 2026

CI Note: E2E timeouts are unrelated to this change

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Additional reproduction — real session bricked (April 12, 2026)

Sequence that triggered it

Key evidence from the SQLite session dump

Why this rules out network/MCP

Why ensureToolIntegrity() would have caught this

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