[cbaucom]

Closes #19

Approach

Aspect ratio (pure-module first): src/timeline-core/aspect.ts owns the decision — ASPECT_RATIOS (16:9 / 9:16 / 1:1) as the single source of truth, dimensionsForAspectRatio (1920×1080 / 1080×1920 / 1080×1080), DEFAULT_ASPECT_RATIO, and an isAspectRatio boundary guard. It is a project-level field in slideshow.json (per PRD: "aspect is a project setting"), not part of the settings cascade, so applying a theme never resets the canvas. PlayerPane lost its hardcoded COMP_WIDTH/COMP_HEIGHT and now takes compositionWidth/compositionHeight props; the composition itself was already dimension-parametric (percent-based Ken Burns, objectFit fit modes), which this slice proves.

PWA: public/manifest.webmanifest + generated PNG icons (scripts/generate-pwa-icons.mjs, rendered from favicon.svg) + a hand-rolled app-shell service worker (public/sw.js): network-first for navigations (cached shell as offline fallback), stale-while-revalidate for same-origin static assets. Media never touches the SW (blob: URLs) and cross-origin (Jamendo) is explicitly bypassed, so neither is ever cached. Registered in PROD builds only. Folder-permission persistence rides on the existing IndexedDB recent-projects + re-grant flow; installing makes Chromium persist the grant.

Acceptance criteria

• Installable; folder reopens with ≤1 re-grant click — manifest (standalone, 192/512 icons incl. maskable) + active SW verified by smoke script; recent-projects re-grant flow unchanged, and installed PWAs get persistent folder permissions per Chromium policy.
• 9:16 on an existing project plays portrait with cover/letterbox/blur-fill correct — smoke opens a project whose slideshow.json says 9:16, asserts the player is exactly 9:16, plays it, and cycles all three fit modes (screenshot below).
• Offline → app shell loads; Jamendo gracefully unavailable — smoke sets the browser offline and reloads; shell renders from SW cache. Jamendo is never cached and its panel already surfaces fetch errors.

Smoke: pnpm build && pnpm preview, then node scripts/playwright-issue-19-smoke.mjs (PROD build required — SW registers in PROD only).

Code review (high effort): APPROVE, zero blocking findings

7 finder angles + verification. One confirmed bug was found and fixed in-branch: aspectRatio from slideshow.json was unvalidated, so a corrupted/hand-edited value (e.g. "4:3") reached dimensionsForAspectRatio's exhaustive switch and returned undefined, crashing the player — now guarded by isAspectRatio with fallback to the default. Notable refuted candidates: title-slide maxWidth: 1600 in portrait (a max-width wider than the container is inert; flex shrink-to-fit + word wrap), Player "remount" on dimension props (same element type/position; primitives), SW serving / for deep routes (single-route SPA, intended shell fallback).

Follow-ups discovered (not in this slice)

• SW cache uses a static CACHE_NAME, so hashed assets from old deploys accumulate until manual eviction; consider build-stamped cache names or LRU trimming.
• MockFileHandle/MockDirHandle/run() are now copy-pasted across three smoke scripts — extract a shared scripts/lib/ helper.
• slidesToJson is up to six positional params; switch to an options object next time it grows.
• RenderPlan doesn't carry canvas dimensions; the future export slice will need to thread them (today the Player gets them from the same slideshow.json source).

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