feat(palace): promote tags/trust/access_count/last_accessed/reinforcements/superseded_by/active to first-class Drawer fields (mp-migration 7/8)

[quangdang46]

Summary

Promote 7 fields previously stored only in Drawer::metadata to first-class typed fields:

Field	Type	Replaces metadata key
tags	Vec<String>	"tags"
trust	Option<String>	"trust"
access_count	u64	"access_count"
last_accessed	Option<DateTime<Utc>>	"last_accessed"
reinforcements	Vec<Reinforcement> (new pub struct)	"reinforcements"
superseded_by	Option<DrawerId>	"superseded_by"
active	bool (default true)	"active"

Motivation

The upcoming MemoryProvider trait methods (PRs 1 + 2 of the migration series) need typed access to these fields:

• boost(&id, amount) / decay(&id, amount) → mutate access_count + last_accessed
• reinforce(&id, session_id, message_index) → push to reinforcements
• supersede(&old, &new) → set superseded_by on old, active = false on old
• tag(&id, tag) / untag(&id, tag) → mutate tags
• link(&from, &to, weight) → doesn't touch these directly but uses same lifecycle

Without typed fields, every trait method would have to do metadata.insert("access_count", json!(...)) round-trips, which is lossy (no type checking), error-prone (typos in key strings), and harder to test.

This is PR 7/8 in the jcode → mempalace Mode C library migration series.

Change

crates/core/src/palace.rs:

• Added 7 fields to Drawer struct, each with #[serde(default, skip_serializing_if = …)] for backwards compat
• New pub struct Reinforcement { session_id, message_index, timestamp }
• Drawer::new initializes all 7 new fields to defaults
• New builder methods: Drawer::tags(Vec<String>) and Drawer::trust(&str)
• New Drawer::migrate_metadata(&mut self) — idempotent, lifts legacy metadata keys to typed fields and cleans the HashMap

crates/core/src/palace/store/usearch_sqlite.rs:

• 2 Drawer { … } literals updated to initialize the 7 new fields (the only pre-existing call sites in the codebase)

crates/core/src/layers.rs:

• 1 Drawer { … } literal updated to initialize the 7 new fields

Tests (crates/core/src/palace.rs:tests):

• drawer_new_field_defaults — all 7 default to expected values
• drawer_typed_builders — .tags([...]).trust("high") work
• drawer_legacy_serde_load — old JSON with metadata-only fields loads cleanly
• drawer_migrate_metadata — legacy keys lifted to typed fields
• drawer_migrate_metadata_idempotent — safe to call twice
• drawer_new_field_serde_roundtrip — typed fields survive serde

Backwards compatibility

Drawers serialised before this change continue to load:

• tags/trust/etc. are absent from the JSON → #[serde(default)] fills them
• The legacy metadata["tags"] value remains in the HashMap until migrate_metadata is called
• No migration is forced on read — call sites that don't care about the new fields work unchanged

Test plan

• cargo test -p mempalace-core --lib → 1133 passed, 0 failed (1499s, includes 7 new tests)
• cargo check -p mempalace-core clean
• cargo fmt --check -p mempalace-core clean
• CI green on ubuntu/macos/windows

Series

#	Title	Branch	Status
6	docs(palace): document Embedder reuse on search_with_embedding	docs/mp-pr6-document-embedder-reuse	merged #16
7	feat(palace): add tags/trust/access_count/reinforcements/superseded_by to Drawer	feat/mp-pr7-drawer-fields	this PR
8	feat(palace): add MemoryProvider::graph_stats_legacy (jcode shape)	feat/mp-pr8-graph-stats-legacy	next
1	feat(palace): add boost/decay/reinforce/supersede/set_metadata to MemoryProvider	feat/mp-pr1-mutation-methods	next
2	feat(palace): add tag/untag/link/list_tags to MemoryProvider	feat/mp-pr2-tag-link	next
4	feat(palace): add MemoryProvider::recent for retention-ranked recall	feat/mp-pr4-recent	next
3	feat(palace): add MemoryScope::All and Wing/Room variants	feat/mp-pr3-scope-variants	next
5	feat(palace): add ActivityEvent sink on PalaceBuilder	feat/mp-pr5-activity-sink	next

🤖 Generated with Claude Code

[quangdang46]

Code already merged via PR #24 (cherry-picked). Closing.