feat(session): Add session detail page

[Amund211]

Summary

A shareable, read-only session detail page at /session/$uuid/detail?date=<ISO>, plus the stats-layer groundwork it needs. It loads a single session from the new flashlight POST /v1/session-at endpoint and renders a full breakdown of that one session, adapted from the design handoff (design/project/Current Session.html) but mapped onto MUI while keeping the design's accent colours / rainbow ribbon.

What's on the page

• Player banner — face avatar, prestige star chip, live/ended badge, started/ended/duration, games count, Share button.
• Tags row — auto-derived from the aggregate: Flawless, Perfect run, On fire, Marathon.
• KPI row — Games (W/L), Win rate (Δ vs lifetime), Session FKDR (Δ vs lifetime), Stars gained.
• Momentum strip — a tile per game with finals, mode dot, minutes, and a W/L/D badge; click to expand a Finals/Beds/Kills/XP detail row with status/accolade chips (Perfect game / Carried / Clutch, Survived / Final death, Bed kept / Bed lost). A trailing-streak indicator sits in the header.
• FKDR trajectory — Recharts line: cumulative session FKDR vs a live lifetime baseline after each game.
• Totals — started/ended/avg game, finals, beds, XP.
• Mode breakdown — solo/doubles/threes/fours/4v4 cards with games, wins, a win-rate bar, and FKDR; click to expand. The 4v4 card and the "Other" bucket (Dreams modes folded into overall) render only when games were played in them.
• Milestones — next stars / next wins / next FKDR, each with "X sessions like this" and projected playtime.
• Highlights — best game, fastest win, session-vs-lifetime FKDR (beating / on par / below), and pace (fk/hr · games/hr).

Data model & derivation

• src/queries/sessionAt.ts — typed client for POST /v1/session-at, returning { session, games }. Each entry in games is a GameSegment { start, end, game } where game is null for a no-game window or an unsplittable multi-game gap. Unknown gamemodes/outcomes are Sentry-reported and dropped.
• src/helpers/sessionDetail.ts — pure derivation (all unit-tested): the session aggregate, per-mode breakdown (including the synthetic "Other" bucket = overall − core modes), the FKDR trajectory, milestones, best/fastest game, and the trailing streak. Per-game data is derived on the client from the consecutive history[] snapshots — the gamemode whose gamesPlayed moved names the game and its stat deltas become the per-game stats.

Stats-layer groundwork (enables the page)

• Split the canonical gamemode list in src/stats/keys.ts into REAL_GAMEMODE_KEYS (solo/doubles/threes/fours/4v4), with ALL_GAMEMODE_KEYS = [...REAL_GAMEMODE_KEYS, "overall"], so the page's mode list has a single source of truth (GAMEMODES reuses it) and adding a mode is a one-line change.
• nextCloseMilestone progression strategy — tighter targets than the regular page (next 10 stars, next 0.5 for ratios, next "half-decade" for counters) so the page's goals feel a session or two out. Milestones reuse computeStatProgression, so targets and ETAs stay in agreement with the regular session page.
• The FKDR trajectory and session aggregate route their ratio stats through computeStat rather than re-implementing ratio math.

Backend contract (matches the flashlight PR)

POST /v1/session-at
{ "uuid": "...", "time": "<ISO>" }

-> {
     "session": { "start": PIT, "end": PIT, "consecutive": bool, "ongoing": bool } | null,
     "games":   [ { "start": PIT, "end": PIT, "game": {...} | null }, ... ]
   }

session === null renders a "No session yet" panel — the empty / 404-ish state for a player who hasn't played a game with Prism running.

URL handling

• Route /session/$uuid/detail with a date search param (Zod z.coerce.date()), following the existing routes' validateSearch pattern so we don't have to URL-encode colons/Z in the path.
• On the first successful response an effect rewrites date to the session's start.queriedAt via navigate({ replace: true }), pre-seeding the cache for the canonical key so there's no refetch. After that the URL is canonical and safe to share.
• A missing or malformed date is coerced to a safe default (degrades to the "No session yet" view) rather than tripping the router's error boundary.
• Share copies globalThis.location.href and shows a "Link copied!" Snackbar (MUI Alert).

Adjacent changes

• Sessions list link — each non-extrapolated row gets a magnifying-glass link to its detail page. Extrapolated rows have no real session start time on the backend (they'd 404), so they render as plain text.
• Layout.tsx — the new /session/$uuid_/detail route is added to useShownPlayer so the shown-player context resolves on the page.

Choices & assumptions

• Search param, not path segment, matching the existing session/history routes.
• Per-game data is derived on the client from consecutive snapshots; a missed snapshot collapses two games into one or surfaces a labelled gap — accepted over a much chattier backend response.
• Lifetime FKDR in the trajectory updates as the session progresses (session vs all-time after each game), matching the design intent rather than a static baseline. The KPI-row "Δ vs lifetime" instead compares against the pre-session lifetime (lifetime at session.start).
• FKDR trajectory numbering — points are numbered by running game count: a real game is G{n}, a multi-game gap spans its range (G5-7), and a no-game window is dropped (it moves no finals) rather than drawn as a flat, mislabelled point.
• MUI primitives over a new design system; MUI Snackbar/Alert instead of adding a toast library.

Tests

• pnpm tsc, pnpm oxlint:check, pnpm oxfmt:check clean.
• Unit — sessionDetail (aggregate, modeBreakdown incl. the "Other" bucket, fkdrTrajectory numbering/labels, computeMilestones incl. blocked/off-pace branches, best/fastest game, trailing streak, inferredGameCount), detailSearch, and nextCloseMilestone (+ strict-monotonic and closer-than-natural properties).
• UI (MSW) — the detail page renders the banner/KPIs/section cards, expands a game tile, normalizes the URL to the session start, and shows the no-session empty state; a mocked POST /v1/session-at handler was added to the shared handlers.

Manual verification (staging)

• Real player with sessions today.
• "No session yet" empty state for a long-idle player.
• Share button copies the canonical (post-normalization) URL.

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