fix: single submit_plan with text/path auto-detect for OpenCode

[backnotprop]

Summary

Collapses the two-tool approach (submit_plan + submit_plan_file) back into a single submit_plan(plan) that auto-detects whether the argument is markdown text or a file path, based on rcdailey's feedback that one tool is sufficient.

Provenance

Version	State	User sentiment
v0.8–v0.12	submit_plan(plan: string) — text-based, uniform across agents	Happy: rcdailey contributed 3 PRs, sfpmld wanted more access, users filed enhancements not bugs
v0.13.0 (PR #318)	submit_plan(path: string) — file-only, 80+ line prompt, TodoWrite warfare	Broke: linxi-1214 blocked, ilmpc confirmed upstream OpenCode prompt change, rcdailey reported leaked file paths
v0.14.0 (PR #329)	Emergency patches — permission overrides, more prompt stripping	Partial fix: permission errors resolved, but agent still writes to repo root, TodoWrite replacements fragile
This PR	submit_plan(plan) — text or path, one tool, ~25 line prompt	Restores happy-state contract + adds file-based revision workflow

How it works

1. First submission: Agent passes plan as markdown text → submit_plan(plan: "# My Plan\n..."). Simple, works from any agent.

2. On deny: Response includes the history path where the plan was saved:

   YOUR PLAN WAS NOT APPROVED.
   Your plan is saved at: ~/.plannotator/history/myproject/auth-2026-03-18/001.md
   You can edit this file to make targeted changes, then pass its path to submit_plan.
   

3. On revision: Agent edits the file with Edit tool (targeted changes, not full rewrite), then calls submit_plan(plan: "/path/to/plan.md"). Auto-detected as file path.

Auto-detection logic

function isFilePath(value: string): boolean {
  return path.isAbsolute(value) && value.endsWith(".md") && existsSync(value);
}

Plan markdown virtually never satisfies all three conditions (absolute path + .md extension + exists on disk).

What changed

• apps/opencode-plugin/index.ts: Single tool, auto-detect, unified ~25 line prompt for all primary agents, removed TodoWrite warfare
• packages/server/index.ts: Surface historyPath through waitForDecision() (the server already saved plans to history via saveToHistory() — just never returned the path)
• packages/shared/feedback-templates.ts: Deny response includes file path hint when historyPath is provided
• packages/shared/feedback-templates.test.ts: Updated test for new wording, added history path test

What's preserved

• stripConflictingPlanModeRules() — still strips "STRICTLY FORBIDDEN" from system prompt
• experimental.chat.messages.transform — still filters "STRICTLY FORBIDDEN" from user messages
• plan_exit suppression via tool.definition hook
• Per-agent .md permission override for plan agent
• Agent switching on approval

Test plan

• bun test apps/opencode-plugin/plan-mode.test.ts — 10 pass
• bun test packages/shared/feedback-templates.test.ts — 6 pass
• Manual: plan agent submits text → review UI → deny → response includes history path → agent edits file → resubmits path
• Manual: Build agent can use submit_plan (uniform access)
• Manual: first submission with text, revision with path, both work

Fixes #328

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