fm-delta - SKILL.md Agent Skill

name: fm-delta description: "Use when the legacy Angular source for an already-migrated page changes (the staleness hook flags drift) — re-migrate only the changed surface via a delta plan, preserving accumulated fixes, then re-enter the gates." argument-hint: " [--app pc|mobile|hana]" user-invocable: true allowed-tools: Read, Write, Edit, Glob, Grep, Bash, Agent

Incremental Re-migration

Re-migrates only what changed when the legacy source drifts, instead of regenerating the whole page — preserving the fixes accumulated through earlier gate loops. All user-facing output in workingLanguage.

Instructions

Step 0: Config & state

Read config (absent → run fm-init; stop). Resolve app, targetDir, appDir, packagesDir, legacyDir, workingLanguage. The page should already be at generated or beyond (else this is a first migration → use fm-analyze/fm-plan/fm-gen).

Step 1: Lock

Acquire docs/migration/{app}/{page}/.lock (stale after 30 min).

Step 2: Compute the delta (planner incremental mode)

Launch migration-planner (Agent) with only its params: mode: "incremental", app, page, analysisPath, planPath (= migration-plan.json, the baseline), legacyDir, outPath = docs/migration/{app}/{page}/delta-plan.json, workingLanguage. It diffs the current legacy source against the analysis.json / migration-plan.json baseline and writes delta-plan.json (added/modified/removed ops + cascade).

Step 3: Offer incremental vs full

Read delta-plan.json.summary. Present:

the change counts (added/modified/removed);
if the delta touches > 60% of the page files, recommend full regeneration (fm-gen) instead; otherwise default to incremental. Let the user choose.

Step 4: Apply

Incremental → launch delta-modifier (Agent) with only its params: app, page, deltaPlanPath (= delta-plan.json), targetDir, appDir, packagesDir, workingLanguage (create ops use tdd-cycle-runner semantics). It applies ops in cascade order and preserves fm-fix edits.
Full → tell the user to run fm-gen {page} (the skill stops here).

Step 5: Record

Patch migration-plan.json/analysis.json with the new baseline; archive the delta as delta-plan.{timestamp}.json.
Update tracker.json (Read-Modify-Write): set status back to generated (the page must re-pass the gates), record deltaAppliedAt.
Release the lock.

Step 6: Report

In workingLanguage: ops applied, tests pass/fail with evidence, confirmation that prior fixes were preserved, and the re-entry point — /frontend-migration-plugin:fm-verify {page} → fm-e2e → fm-parity.