GH-2409: fix(executor): OpenCode response parsing decodes wrong fields — silent empty Output

[alekspetrov]

Summary

Automated PR created by Pilot for task GH-2409.

Closes #2409

Changes

GitHub Issue #2409: fix(executor): OpenCode response parsing decodes wrong fields — silent empty Output

Summary

After PR #2408 lands, the schema rejection at first send is gone, but OpenCodeBackend.sendMessage then mis-parses the success response. Pilot will see Success: true with empty Output, leading to no commit / empty PR / silent failure downstream.

Evidence (verified against OpenCode v1.4.6 source)

packages/opencode/src/server/instance/session.ts:854-895:

.post("/:sessionID/message",
  describeRoute({
    responses: {
      200: { content: { "application/json": { schema: resolver(
        z.object({ info: MessageV2.Assistant, parts: MessageV2.Part.array() })
      ) } } },
    },
  }),
  ...
  async (c) => {
    c.status(200)
    c.header("Content-Type", "application/json")
    return stream(c, async (stream) => {
      const msg = await ...svc.prompt(...)
      stream.write(JSON.stringify(msg))
    })
  },
)

So the success response is:

• Content-Type: application/json (not text/event-stream — the Accept: text/event-stream header sent by Pilot is ignored)
• Body shape: {info: MessageV2.Assistant, parts: MessageV2.Part[]}

Pilot's current parse path (internal/executor/backend_opencode.go:243-256):

} else {
    var msgResult struct {
        Success bool   `json:"success"`
        Output  string `json:"output"`
        Error   string `json:"error"`
    }
    json.NewDecoder(resp.Body).Decode(&msgResult)
    result.Success = msgResult.Success
    result.Output  = msgResult.Output
    result.Error   = msgResult.Error
}
if result.Error == "" { result.Success = true }

None of success/output/error exist on OpenCode v1.4.6's response. All three decode to zero values → result.Output = \"\" → final Success = true (because Error is empty).

Impact

• Reporter of OpenCode backend fails right after server is ready (message payload/schema mismatch) #2407 sees running rather than failure after PR fix(executor): support modern opencode message schema #2408 → the HTTP call succeeds but Pilot extracts no useful content.
• Downstream: empty Output, no commit, autopilot sees nothing to push.

Fix (sketch)

Map the actual response shape:

type ocAssistantMessage struct {
    Info  ocAssistantInfo `json:\"info\"`
    Parts []ocPart        `json:\"parts\"`
}
type ocPart struct {
    Type string `json:\"type\"`
    Text string `json:\"text,omitempty\"`
    // tool, file, agent, subtask variants
}

Then concatenate text parts into result.Output, surface tool-use parts as BackendEvents via opts.EventHandler (mimicking the streaming path), and pull token usage from info.

Alternative: switch to POST /session/:sessionID/prompt_async (returns 204 immediately) and consume the SSE event stream from /event for per-token deltas. That endpoint actually streams; the current synchronous /message endpoint never does despite the misleading description: \"...streaming the AI response\".

Repro (post #2408)

1. Configure Pilot with OpenCode 1.4.x backend.
2. Pick up a labeled GitHub issue.
3. Wait through OpenCode execution (will run for minutes).
4. Observe: HTTP 200 returned, but Pilot reports success with no commits / no PR content.

References

• OpenCode v1.4.6 message route
• OpenCode v1.4.6 PromptInput / Assistant message types
• Found while reviewing fix(executor): support modern opencode message schema #2408 / OpenCode backend fails right after server is ready (message payload/schema mismatch) #2407.

[codecov-commenter]

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Codecov Report

❌ Patch coverage is 76.92308% with 15 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
internal/executor/backend_opencode.go	76.92%	11 Missing and 4 partials ⚠️

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