Docs, ticks, working app

tickets/026-max-logs-in-memory.md

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+# 026 — Settings: maximum logs kept in memory
+
+## Summary
+
+ottyl currently keeps every ingested log forever in the in-memory `BTreeMap`. The
+wishlist wants a settings-configurable cap on how many logs are retained, with no
+cap (unlimited) as the default.
+
+## Scope
+
+- New `Settings` field (e.g. `max_logs: Option<usize>`), `None`/unset = unlimited,
+  matching the existing "by default it should be unlimited" requirement.
+- Enforce the cap in the engine's ingest path: once the `IngestedLog` range
+  exceeds the configured max, evict the oldest entries (lowest `sequence`) to
+  bring it back under the cap.
+- Decide and document what happens to data that references evicted logs:
+  - Params/metrics already derived into `Bucket` values from an evicted log are
+    **not** retroactively removed (buckets are aggregate data, not raw logs) —
+    state this explicitly so it's not treated as a bug later.
+  - `sequence` numbering does not reset/renumber on eviction.
+- Expose the setting in the Settings API/NavMenu settings panel (a numeric input,
+  clearable back to "unlimited").
+
+## Acceptance criteria
+
+- With no cap configured, behavior is unchanged (unbounded retention, as today).
+- Setting a cap and ingesting past it keeps memory usage bounded — oldest logs
+  are evicted, newest `max_logs` remain queryable via `GET /api/logs`.
+- Changing the cap at runtime (via settings) takes effect on the next ingest
+  without requiring a restart.
+
+## Depends on
+
+None — extends the existing `Settings` model.