fix: keep orphaned linked memories visible in the timeline

[petra-dot]

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

[lindixu6-hash]

Reviewed the timeline pairing path and the new regression coverage. The change preserves complete memory/prompt ordering and moves only one-sided pairs into the existing timestamp-sorted standalone list.

Local verification on c7b705fe6073517aa2611ea118f57d8dc1d1a232: targeted orphan/pair tests 2 pass, 0 fail; bun run typecheck passed; bun run format:check passed. The sandbox reported cleanup restrictions for temporary directories after the commands completed, so those restrictions did not affect the assertions or static checks.

[lindixu6-hash]

Post-merge validation for exact merge commit 93cb1cf81049cbed785837507bc4b1a57445e5a9: Platform Package Smoke run 32276470861 passed all six jobs (Ubuntu, Windows, macOS 15/26 on Apple Silicon, and macOS 15/26 Intel). Each job completed dependency installation, typecheck, production build, the full test suite, package creation/install, and native/runtime smoke checks.