feat(session): add anti-drift session notes

[vicary]

Summary

• Redesign memory around a search-first architecture where session_search() is the canonical recall API and injected XML is only a bounded hint surface.
• Add durable session notes without TTL, freshness-aware note ranking, timestamped note hits, and same-project delete-by-id cleanup.
• Introduce normalized memory result contracts, dream summary storage/job scaffolding, detached shutdown proof coverage, and updated smoke-test documentation for the new model.

Design

Authority Model

• opencode db / SQLite is the exact chronological source of truth for user turns, assistant turns, and tool calls.
• Redis/FalkorDB stores derived local artifacts and operational state, not duplicate exact transcript authority.
• Graphiti remains asynchronous enrichment and a one-off hint source; it is not on the hot path and is not the authoritative memory reader.

Canonical Recall Path

• session_search() becomes the default memory read API.
• Query mode accepts query plus optional when, searches normalized exact/history, notes, and summaries, and returns exact-style results before summaries.
• Reflection mode is represented by an empty query and returns chronological summaries around when.
• Results use a shared normalized model with type: "entry" | "note" | "summary", ref, snippet, score, created_at, and optional metadata.

Injection Contract

• Injected continuity now uses one top-level <memory version="2"> wrapper.
• <persistent_memory> is nested inside <memory> instead of being a separate top-level block.
• Exact entries are never injected; exact recall must go through session_search().
• Compaction/startup continuity may include bounded summaries and up to 10 current-session notes, but not raw exact entries.
• Legacy <session_memory> expectations were updated in tests to the normalized <memory> envelope.

Durable Session Notes

• Session-local note hashes no longer receive TTLs, and reads no longer refresh note TTL.
• Project note metadata now records last_read_at on successful session_notes_read(id) calls.
• session_search note hits expose created_at and updated_at, but not last_read_at.
• Note ranking now uses relevance multiplied by write freshness and bounded read freshness.
• Same-project sessions may delete obsolete notes by id, while non-empty replacement remains ownership-conservative.

Dream Summary Layer

• Adds local dream summary/job scaffolding for durable summary artifacts.
• Dream summaries are intended as lossy chronological hints for reflection and injection, not exact transcript truth.
• Shutdown handoff now has proof-only detached worker coverage plus explicit warning fallback behavior when detached work cannot be started safely.

Graphiti Role

• Graphiti remains optional and asynchronous.
• Graphiti-derived material is treated as hint-only summary material.
• If a Graphiti hint matters, agents should reconnect to exact evidence through session_search().

Retention Model

• Durable memory artifacts such as notes and summaries do not expire by TTL.
• Operational state remains bounded separately.
• Staleness is handled by ranking and relevance rather than deleting useful memory by age.

Implementation Notes

• Added normalized memory result types and memory-search orchestration.
• Updated session_search schemas and runtime wiring for normalized ref / refs responses and optional when.
• Updated note storage, note search, note read metadata, note delete semantics, and entrypoint wiring.
• Updated message/compaction scrubbing and assertions for the <memory version="2"> wrapper.
• Added dream store, dream runner, dream job, detached-worker proof, and shutdown warning coverage.
• Updated smoke tests and design/implementation docs for the search-first unified memory direction.

Test Plan

• deno test -A
• deno task check
• deno task lint
• deno task fmt --check

Latest full-suite verification before commit: 66 passed (692 steps), 0 failed.