feat(vision): resolve persisted image URLs against the API base

Images are now stored on disk under tmp (not SQLite) and served via
GET /images/:conversationId/:imageId. Persisted ImageChunk.url is a compact
relative HTTP path (/images/<conv>/<uuid>.png) instead of a base64 data URL.
No wire/transport-contract type change (behavior only) — re-mirrored the
delta notes.

- New pure resolveImageUrl(url, apiBase) helper (core/chunks/image-url.ts,
  +8 tests): data/absolute URLs pass through; relative paths are prepended
  with the API base (no double slash; empty base -> root-relative). Exported
  from core/chunks + re-exported from features/chat.
- ChatView: new apiBaseUrl prop; <img src> uses resolveImageUrl. The
  optimistic echo's data URL passes through; persisted relative paths
  resolve against the base. +3 tests.
- AppStore exposes httpBase (getter); App.svelte passes apiBaseUrl into
  ChatView and the heartbeat RunModal (also renders image chunks).

Verification: svelte-check 0/0; vitest 959/959 (run twice, +11); biome
clean; vite build OK. See backend-handoff.md §2j-update-2.

Not merged or pushed.

1 files changed, 8 insertions, 0 deletions

diff --git a/.dispatch/transport-contract.reference.md b/.dispatch/transport-contract.reference.md
index 047f050..182279a 100644
--- a/.dispatch/transport-contract.reference.md
+++ b/.dispatch/transport-contract.reference.md
@@ -27,6 +27,14 @@
 > `PUT /settings/vision` ← `SetVisionSettingsRequest` (partial: `imageLimit?` non-negative int, 0 = disable
 > compaction; `compactionModel?` `<key>/<model>` or null = auto). See `backend-handoff.md` §2j.
 >
+> **2026-06-26 update (image storage — NO type change, behavior only):** persisted `ImageChunk.url`s are now
+> compact relative HTTP paths (`/images/<conversationId>/<uuid>.png`) served by the new
+> `GET /images/:conversationId/:imageId` endpoint (raw image bytes + correct Content-Type) — NOT base64 data
+> URLs (images are stored on disk under tmp, not in the SQLite store). `ChatRequest.images` (`ImageInput.url`)
+> is UNCHANGED — clients still send data URLs; the backend saves them to tmp and returns compact paths in
+> the persisted chunks. A client resolves a relative `url` against its API base (`resolveImageUrl`); the
+> optimistic echo's data URL and any absolute URL pass through. See `backend-handoff.md` §2j.
+>
 > **2026-06-25 delta (SSH handoff #2 — ADDITIVE to `[email protected]`, NO version bump):** adds the
 > computer HTTP API types: `ComputerListResponse` (`GET /computers`), `ComputerResponse` (`GET /computers/:alias`),
 > `ComputerStatusResponse` (`GET /computers/:alias/status`), `TestComputerResponse` (`POST /computers/:alias/test`),