Phase 5b slice A. Generic TTL cache that replaces the mechanically
identical dashboardCache + timelineCache in slices B/C.
- TTLCache[V] over map[string]entry[V] with sync.RWMutex.
- Get / Set / Invalidate(key) / InvalidateAll.
- Lazy expiry — a Get past the deadline removes the entry; no sweeper
goroutine (matches today's behaviour and stays simple at single-user
scale).
- Nil receiver is safe across all four methods — same defensive shape
the existing per-package caches use.
Tests cover empty Get, Set+Get, expiry on miss, overwrite,
keyed-Invalidate isolation, InvalidateAll, nil receiver, pointer
payload behaviour, and a -race-flag concurrent-access probe across
8 workers × 200 ops.
No web/mcp wiring yet — slices B/C migrate the callers. Same Go
linker DCE caveat as 5a slice A applies (strings | grep alone won't
fire on this slice).
Task: t-projax-5b-cache
mAi
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