feat: explicit associations on remember + session handoff tool

[CalebisGross]

Explicit associations on remember

The encoding agent discovers associations automatically, but sometimes the caller knows the relationship at write time. For example, when storing a decision that directly relates to a prior error, the association is obvious.

Proposed: Add optional associate_with parameter to remember:

{
  "text": "Chose approach B because approach A failed",
  "type": "decision",
  "associate_with": [
    {"memory_id": "abc-123", "relation": "caused_by"}
  ]
}

These explicit associations would be created immediately alongside the raw memory, before async encoding. The encoding agent can still discover additional associations.

Session handoff tool

Session handoff notes are the most valuable cross-session context. Currently they're freeform remember calls with no structure. A dedicated tool would enforce a useful format and make handoffs retrievable.

Proposed: create_handoff MCP tool:

{
  "completed": ["Merged PR #295", "Fixed theme extraction"],
  "pending": ["Test context_boost end-to-end"],
  "to_test": ["get_context metrics in JSON format"],
  "known_issues": ["Path leakage in themes"],
  "next_session_hint": "Start by merging release PR"
}

Stored as type handoff with high salience. recall_project would surface the most recent handoff automatically.

Why together

Both extend the remember / memory creation path in internal/mcp/server.go and internal/store/.

[CalebisGross]

Fixed in PR #313 — remember now accepts associate_with param (array of {memory_id, relation}). Explicit associations stored in raw metadata, created by encoding agent alongside auto-discovered ones (strength 0.9). New create_handoff tool stores structured session notes with 0.95 salience.