fix: keep orphaned linked memories visible in the timeline - #260

Bug

handleListMemories (the Web UI timeline endpoint) grouped memory-prompt pairs by id and then dropped any pair missing one side. A memory whose linked prompt was deleted (DELETE /api/prompts/:id without cascade), expired, or never captured, vanished from /api/memories even though it still existed in the shard and was still reachable via /api/search. Same for prompts whose linked memory was gone.

Root cause

In handleListMemories:

const pairs = Array.from(linkedPairs.values())
  .filter((p) => p.memory && p.prompt)   // <- one-sided pairs discarded

Items that referenced a missing counterpart were neither in pairs nor added to standalone.

Fix

One-sided pairs now fall back to standalone, so orphaned linked memories/prompts still render, unlinked, in the timeline. Complete pairs still render together.

Tests

• memory timeline listing > keeps memories whose linked prompt is missing from the timeline — reproduces the drop (fails before the fix, passes after)
• memory timeline listing > renders linked memory-prompt pairs together in the timeline — guards the pairing path

Verification

• tsc --noEmit clean
• Full suite: 407 pass / 4 fail, identical failure set on clean main (pre-existing flakes: onnxruntime-resolve shim, plugin-loader contract timeout, turso-shard recreate timeout, config parallel). No new failures.
• Prettier clean