openspec: propose route-surface-breakdown

Surface + waytype proportion bars on route detail, from the BRouter waytags the
Planner already computes (and currently discards on save). Design records the
data-source decision: persist a compact distance-weighted breakdown for
Planner-created routes (accurate, no external call); Overpass map-matching for
imports/uploads is parked as a future option.

Validates with `openspec validate --strict`. Specs only; no code.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

openspec/changes/route-surface-breakdown/design.md

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+## Context
+
+The Planner computes accurate per-coordinate surface/highway from BRouter's
+`messages`/`WayTags` (`apps/planner/.../route-merge.ts` → `EnrichedRoute`), and
+`ColoredRoute` already renders the route coloured by surface. But this metadata
+is **session-only**: the planner→journal handoff (`api.save-to-journal`) POSTs
+only `{ gpx }` to the Journal callback (`api.routes.$id.callback`), the `routes`
+table has no surface column, and GPX carries no surface extensions. So today no
+saved route has surface data.
+
+## Goals / Non-Goals
+
+**Goals**
+- Surface + waytype proportion bars on route detail, using data we already
+  compute, with no new external dependency.
+
+**Non-Goals (v1)**
+- **Activities / imported / manually-uploaded GPX** — they have no waytags
+  (bare GPX). They show no breakdown for now (see "Data source" → future
+  Overpass).
+- **Colouring the Journal map line by surface** — needs per-segment data, not
+  just the summary; a clean follow-up once the bars land.
+- Selectable surface-vs-waytype toggle UI beyond showing both bars.
+
+## Decisions
+
+### D1: Data source — persist BRouter waytags at save (Planner routes only)
+Two ways to get a breakdown onto the Journal detail page:
+
+- **(A, chosen) BRouter-at-save** — the Planner already has 100%-accurate
+  per-segment surface/highway; compute the distribution there at save and
+  persist it. Accurate, cheap, no external call. **Limitation:** only
+  Planner-created routes (activities/uploads have no waytags).
+- **(B, future) Overpass map-matching** — snap arbitrary route geometry to OSM
+  ways and read `surface`/`highway` server-side. Covers imports/uploads, but
+  it's expensive, approximate, rate-limited, and an external dependency. Parked
+  for when we want imports covered (the repo already proxies Overpass for POIs).
+
+v1 ships (A). Routes without the data degrade to no bars.
+
+### D2: Store a compact distance-weighted summary, not per-segment data
+The bars need **proportions**, not geometry. At save, sum the haversine length
+of each coordinate segment into its surface bucket (and highway bucket),
+yielding `{ surface: { asphalt: <m>, gravel: <m>, … }, highway: { … } }`
+(metres per category). This is tiny (a handful of keys), stored as a nullable
+`surface_breakdown` jsonb on `routes`. Per-segment data (for future map line
+colouring) is deliberately *not* persisted in v1 — that's a bigger payload and
+a separate feature.
+
+### D3: Handoff carries it
+`api.save-to-journal` adds `surfaceBreakdown` to the POST body alongside `gpx`;
+the Journal callback validates (Zod, all values ≥ 0) and stores it. The field
+is optional, so the handoff stays backward-compatible and non-Planner callers
+(if any) are unaffected. Re-saving a route recomputes/overwrites it.
+
+### D4: Rendering
+A `SurfaceBreakdown` component renders one horizontal stacked bar per dimension
+(surface, then waytype): segments sized by percentage, coloured via
+`SURFACE_COLORS` / `HIGHWAY_COLORS` (`DEFAULT_*` for unknown), with a legend
+listing each category + km + percent (largest first). Unknown/unmapped tags
+collapse into an "other" segment. Hidden entirely when `surface_breakdown` is
+null or empty. Labels via i18n; distances via `stats.ts`.
+
+## Risks / Trade-offs
+
+- **Coverage gap** — only Planner routes get bars in v1. Acceptable: routes are
+  *designed* in the Planner, which is exactly where "how much gravel" matters.
+  Imports get bars later via (B).
+- **Tag sparsity** — OSM `surface` is often missing; those segments bucket as
+  `unknown`/"other". We show it honestly rather than guessing.
+- **Stale on edit** — editing a route's geometry elsewhere without re-routing
+  could leave the breakdown stale; recomputing on every Planner save keeps it
+  fresh for the normal flow.