feat(plugin): copy-as-prompt button — deterministic fix prompt for Figma AI agent #587

Motivation

Figma now ships a native AI agent in the editor. The plugin can close the fix loop for designers who don't have Claude Code + MCP access (the current canicode-roundtrip path requires a full seat + Claude Code session):

1. Analyze in the plugin
2. Copy a deterministic fix prompt
3. Paste it into Figma's AI agent, which performs the fixes / asks the gotcha questions
4. Re-analyze in the plugin to verify

This is the lint --fix experience, delegated to the host agent. Consistent with ADR-013: canicode diagnoses and prompts the fix direction, but does not own fix execution.

UX (intentionally minimal)

• One "Copy fix prompt" button at the top of the plugin report
• Clicking opens a popup/modal with the prompt in a read-only textarea + copy button (textarea doubles as a manual select-copy fallback for Figma's plugin iframe clipboard restrictions)
• The prompt always contains everything in the current report — no chunking, no "next batch" state. The plugin stays stateless; re-analysis after the agent's fixes naturally regenerates the remaining prompt
• Selection-size warning (one inline line): triggered by selection node count (default ~1000 nodes, constant in config), NOT issue count — real designs produce dozens of issues even at proper section scope, so issue count is a bad proxy for "scope too big". Warning only; never blocks

Prompt content (all deterministic — pure templating, no LLM call)

• Violation rules → imperative fix instruction per rule template, with node name + id (e.g. "Frame 'Card' (12:34) has no auto-layout — apply vertical auto-layout, gap 8")
• Info-collection (gotcha) rules → instruct the agent to ask the user, in its own designer-friendly phrasing, based on the rule context — we do NOT author the question text. E.g. "Node X has no interaction states defined. Ask the user what hover/pressed should look like, then record the answer as an annotation on the node"
• Annotation format spec: the gotcha section must specify the exact annotation convention canicode reads (same format as the roundtrip annotation upsert), otherwise re-analysis cannot detect the gotcha as resolved and the verify loop never closes
• Optional: sort structural fixes (e.g. no-auto-layout) first within the prompt, since structural changes can invalidate other findings

Scope

• src/core/: prompt-builder module — pure function (violations, gotchas) → prompt text, per-rule template registry next to rule messages. Lives in core so web/CLI reports can reuse it later
• app/figma-plugin/: copy button + modal with read-only textarea
• Selection-size warning line + node-count threshold constant

Out of scope

• Chunking / batching / "next bundle" state — explicitly rejected for simplicity; scope control is the user's job via selection
• Authoring gotcha question text — the agent phrases questions itself
• Any gotcha Q&A UI in the plugin

🤖 Generated with Claude Code