feat(trail): add trail recording with pause/resume and GPX 1.1 export

[jasoneplumb]

Closes #77

Summary

• Trail recording state machine (idle → recording → paused → idle) with real-time polyline rendered on the map
• Start, pause, resume, stop controls in the bottom-right recording panel; record button disabled until location is active
• GPS accuracy filter (>30m discard) and distance threshold (<5m skip) on every fix
• GPX 1.1 auto-download on stop: multi-segment support preserves pause gaps as separate <trkseg> elements; <ele> tag now populated from device altitude when available
• Stats bar shows elapsed time, distance, and speed during recording

Test plan

• Enable location, tap Record — polyline appears and stats bar shows
• Tap Pause — dot turns amber, stats freeze; tap Resume — new segment begins (no straight-line gap artifact)
• Tap Stop → confirm dialog → GPX file downloads as track-YYYY-MM-DD-HHmm.gpx
• Import GPX into Strava or AllTrails — track renders correctly
• On a device with barometric altitude, verify <ele> values appear in GPX

🤖 Generated with Claude Code

[claude]

Code Review

This is a clean, well-scoped PR. The altitude feature is added with minimal footprint across exactly the right three files. A few observations:

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What looks good

Type propagation is consistent. altM?: number is added to both trailPoints and trailSegments in types.ts, and the optional is threaded cleanly through appendTrailPoint and formatPoint. Nothing is left half-wired.

GPX element ordering is spec-compliant. GPX 1.1 schema requires <ele> before <time> inside a <trkpt>, and ${eleTag}${timeTag}${speedTag} respects that order.

Null → undefined conversion is the right pattern. e.altitude !== null ? e.altitude : undefined correctly maps the browser's null-when-unavailable into TypeScript's optional semantics.

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One concern worth verifying

e.altitude is typed as number in Leaflet's LocationEvent, not number | null. With strict mode + noUncheckedIndexedAccess, TypeScript may flag e.altitude !== null as always-true, or the compiler may silently accept it since number !== null is always true at the type level (meaning the undefined branch is dead code from TypeScript's perspective).

Run npm run type-check to confirm it passes cleanly. If the Leaflet types have been patched locally to reflect the real-world nullable behavior this is already handled; if not, you may want a type assertion (e.altitude as number | null) to make the intent explicit and keep the runtime guard without confusing future readers:

const altM = (e.altitude as number | null) !== null ? e.altitude : undefined;

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Minor nit

altM is appended as the last parameter to appendTrailPoint, after the already-established state and map parameters. That's the right call for an additive optional — no callers need to change and the signature stays readable. No action needed, just confirming this was intentional.

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Summary

The implementation is correct and the scope is tight. The only thing worth a quick double-check is whether tsc is happy with the e.altitude !== null guard given Leaflet's non-nullable type declaration. Everything else looks solid.

[claude]

Code Review

The previous review flagged the Leaflet type mismatch on e.altitude (typed number, null at runtime). This iteration already addresses that with the explicit cast — good follow-through.

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What looks good

Previous concern resolved. (e.altitude as number | null) !== null ? e.altitude : undefined makes the intent explicit and keeps the runtime guard legible. TypeScript won't complain about a redundant null-check and future readers understand why the cast is there.

GPX spec compliance confirmed. GPX 1.1 requires <ele> before <time> inside <trkpt> — ${eleTag}${timeTag}${speedTag} is correct.

altM?: number threads cleanly. Both trailPoints and trailSegments in types.ts are updated in lockstep, appendTrailPoint takes it as a trailing optional (no existing callers affected), and formatPoint destructures it correctly.

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One informational note (no action required)

e.altitude from the Geolocation API is WGS84 ellipsoidal height — altitude above the mathematical ellipsoid, not above sea level (MSL). Consumer GPS devices often report ellipsoidal height, which can differ from MSL by 10–100 m depending on location. Strava and AllTrails both accept WGS84 altitude in GPX files without issue, so this won't break import; just worth documenting if users ever question elevation discrepancies vs. topo maps.

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Summary

Clean, minimal PR. The scope is tight (10 additions, 6 deletions across exactly the right three files), the previous review concern is addressed, and the GPX output is spec-compliant. No blockers.