submit_plan fails in plan-agent mode from Opencode after 0.19.18

[TonyReg]

Summary

submit_plan appears broken when invoked through the allowed plan agent path from Opencode.

Direct orchestrator calls are correctly blocked in plan-agent mode, but once the request is routed through the plan agent, the initial submit still fails before the review flow starts.

This seems related to Opencode integration and started after the 0.19.18 changes in Plannotator.

What works

• Direct orchestrator call is rejected as expected in plan-agent mode:
  • submit_plan can only be called by: plan
• Invoking the flow through a plan agent does reach submit_plan

What fails

The first submit_plan call fails against an empty backing file with:

• Error: end (1) exceeds file length (0)

We also retried using the documented first-call payload shape:

{
  "edits": [
    {
      "start": 1,
      "content": "# Smoke Test Plan\n\n1. Verify initial submit works.\n2. Confirm whether the review flow responds.\n"
    }
  ]
}

That still behaved as if end: 1 were present and failed with the same error:

• Error: end (1) exceeds file length (0)

Expected behavior

For the first submit_plan call on a new backing file, a single edit with start=1 and content only should succeed and start the normal review/approval flow.

Actual behavior

The plan-agent path appears to inject or normalize the payload in a way that behaves as though end is set on the initial call, causing validation to fail before the review flow appears.

Repro notes

• Environment: Opencode
• Workflow: Plannotator plan-agent mode
• No repo files or Plannotator config were changed during testing
• This did not look like a permission/configuration issue; it looked like a wrapper/serialization issue in the plan-agent path

Suspected regression window

Started after the 0.19.18 changes in Plannotator.
OpenCode 1.15.4

[backnotprop]

Im reverting the previous release, and cutting a new one in 0.19.19 its in the release pipeline now

[backnotprop]

@rcdailey im patching by reverting #730 ... once we have clean fix I can get it back in

[backnotprop]

Patch is released, @plannotator/opencode@0.19.19 (latest should updated for opencode)

[rcdailey]

Opened #752 with the clean fix. The issue is in validateEdits rejecting end > lineCount when lineCount === 0 (empty backing file on first call). The plan-agent path includes end in the payload even when the agent omits it, so validation fails before applyEdits ever runs.

applyEdits already handles this correctly (splice clamps on an empty array), so the fix just skips the bounds check when lineCount === 0. Added test coverage for the scenario.