Depends on: #151 (shipped — this story revises one of its decisions). ## Goal The dashboard's lifetime chart gains the standard chart interactions: a zoom control (+/− buttons), drag panning, double-click / pinch / keyboard zoom — like every other chart in the app. ## Context The chart is a **fixed overview on purpose** (#151): `stats/map.ts` re-simplifies the whole logbook's geometry at ~1 device pixel for the one zoom fit-to-bounds gives it (`simplifyToleranceForBBox`, `CHART_TARGET_PIXELS`), and `MapCanvas`'s `interactive: false` — with the lifetime chart as its only caller — removes pan and zoom so a viewer can never see the facets that tolerance would show. The rule is written down in three places: `apps/web/src/map/MapCanvas.tsx`, `apps/api/src/modules/stats/map.ts`, and `docs/DESIGN.md` → Screen patterns → Logbook. So this is a two-sided change, not a flag flip: - **Flipping `interactive` alone** ships faceted lines — the exact outcome the fixed design exists to prevent. Rejected. - **Re-fetching geometry per zoom/bbox** gives unlimited zoom but costs a request and a server-side simplification pass per zoom step; the single-payload design is the stated reason the route is viable at all on this host. Rejected — a viewer who wants more than a few levels of detail has the voyage's own full-resolution chart one legend click away. - **Chosen: bounded headroom.** Serve geometry simplified for fit-to-bounds **plus K zoom levels** (proposed K = 3, i.e. tolerance ÷ 2³), and cap zoom-in at fit + K. The viewer can zoom into a cruising area without ever outrunning the geometry; payload grows by at most ~2^K; the request count stays one. ## Scope **API — `GET /api/v1/stats/map`.** - `simplifyToleranceForBBox` targets fit-to-bounds + K levels (equivalently: `CHART_TARGET_PIXELS × 2^K`). The floor stays `SIMPLIFY_TOLERANCE_M` (15 m — finer than the stored geometry buys nothing); re-derive whether `CHART_MAX_TOLERANCE_M` still binds under the new formula and fix its comment either way. - K lives in `@seamark/contracts` as a shared constant, imported by both the server (tolerance) and the SPA (zoom cap), so the two sides agree by construction — the #174 lesson, one figure, one home. - Statement count and purity are unchanged; the existing tests keep pinning both. - Measure the payload (bytes and point count) before/after on a real logbook and record the figures in the commit message; if the growth argues K down, tune K, not the design. **SPA — `LifetimeMap` / `MapCanvas`.** - The lifetime chart renders interactive: drag pan, +/− zoom control, double-click, touch, keyboard. **Scroll-wheel zoom stays off** — that is an app-wide embedded-chart rule, not part of this story. - Zoom-in is capped at fit-to-bounds + K (the shared constant). Zoom-out and pan are unrestricted; `FitBounds` already keeps the user's view across re-renders that frame the same extent. - The chart keeps its exact fractional fit (`zoomSnap: 0`) — underfill is what that setting fixed, and +/− buttons step whole levels from a fractional base perfectly well without a scroll wheel. This decouples `zoomSnap` from `interactive` in `MapCanvas`. - With its only caller gone, `interactive: false` is dead code: remove the prop and rework the docblock that argues for it, rather than leaving an escape hatch nothing uses. - **Still no harbour markers, at any zoom** — the no-chips rule (#151) is about count (hundreds of harbours), not zoom, and the legend stays the way to a voyage's detail. ## Acceptance criteria - The dashboard chart pans by drag and zooms via the control, double-click, pinch, and keyboard; the scroll wheel still scrolls the page. - Zoom-in stops at fit + K, and at that zoom the drawn lines show no visible faceting on a real logbook (served tolerance ≲ 1 device px there by construction). - The initial framing is pixel-identical to today: exact fractional fit-to-bounds over the same extent. - One request, statement count unchanged, `stats.map` response contract-valid; the server stays pure and deterministic. - Legend↔chart hover coupling works while zoomed and panned. - Payload before/after figures recorded in the commit message. - `pnpm typecheck` / `check:policy` / `test` green. ## Docs Every statement of the fixed-overview rule is re-derived, not left contradicting the shipped behaviour: `docs/DESIGN.md` (Logbook screen pattern), the `MapCanvas.tsx` and `stats/map.ts` docblocks (both argue the fixed design at length), and `docs/API-CONTRACTS.md` for the shared K constant if it surfaces there.