feat: v0.2.0 delegation resilience (caching, retry+fallback, custom prompt, inline switch)

[rz1989s]

v0.2.0 — Delegation Resilience

Closes PRD gaps #2–#5. Builds on the v0.1.0 capability-aware core with four DELEGATE-mode resilience layers. SPEC-2 + PLAN-2 in the strategy vault.

What's new

• Caching (gap fix: v0.2.1 Mac-friendly hotkey (ctrl+shift+i) + cache-show clarifier #2) — content-addressed cache (key = sha256 of source-image hash + compression params + prompt + vision model + reasoning). A second describe_image on the same image costs zero vision-model API calls. In-memory by default; optional persisted disk cache (LRU-evicted). Only successes cached. lib/cache.ts.
• Custom system prompt (gap feat(v0.3.0): paste UX — markers + auto-delegation wiring #3) — configurable framing prepended to the vision-model request. Panel row (inline Input edit) + /vision system-prompt (multi-line via ctx.ui.editor).
• Retry + fallback (gap fix(v0.3.1): handle escaped-space paths (macOS screenshot drag-paste) #4) — retryable errors (5xx/429/network) retried with exponential backoff (abort-aware via ctx.signal); non-retryable + exhausted → configured fallback vision model (one attempt). Full error classification. lib/resilience.ts.
• Inline model switch (gap fix(v0.3.2): use globalThis for shared state (jiti dual-module-instance bug) #5) — alt+shift+v hotkey (pi.registerShortcut) + /vision-use command; both open the vision-model picker or set directly.

Changes

• lib/image.ts — sourceHash (sha256 of original bytes) on ImageLoadResult
• lib/cache.ts — NEW: VisionCache (memory Map + optional disk LRU), cacheKey
• lib/resilience.ts — NEW: withRetry, sleep (abort-aware), classifyError, AbortError
• lib/config.ts — 8 new fields (forward-compatible — v0.1.0 config loads as-is)
• lib/delegate.ts — cache lookup before call, system prompt, retry+fallback pipeline, abort-aware
• extensions/vision.ts — 7 new panel rows, 5 new /vision subcommands, /vision-use, alt+shift+v

Verification

• 154 tests pass (was 92) — pnpm typecheck clean
• T11 cache hit = 0 calls ✅, T16 system prompt ✅, T18 retry on 500 ✅, T20 4xx→fallback ✅, T24/T25 hotkey + /vision-use ✅
• v0.1.0 regression: SPEC-1 T1–T10 still green
• Tarball clean (tests excluded; 26KB packed)
• Clean-room; no AI attribution

After merge: git tag v0.2.0 → CI auto-publishes @getpipher/vision@0.2.0.