[STAGING — DO NOT MERGE AS-IS] retrieval port + open-core scaffolds (split into reviewable PRs)

[ohdearquant]

⚠️ STAGING BRANCH

Do not merge this PR as-is. This is a staging snapshot for tomorrow's review. Ocean and λ_khive will split this into individually reviewable PRs per concern before any merge to main.

What's in this snapshot

1. Retrieval port from khive-internal/platform/retrieval

Verified, formally-proof-paired implementation ported into OSS as 4 separate crates (one crate ↔ one proof tree):

• khive-hnsw — HNSW with INT8 quantized two-phase search (~9K LOC + tests)
• khive-bm25 — Okapi BM25 with deterministic scoring (~5K LOC + tests)
• khive-fusion — RRF + Weighted + Union fusion strategies (~1.5K LOC + tests)
• khive-retrieval — hybrid composer over the above (~12K LOC + tests)

Plus khive-fold/src/objective/registry.rs (NEW — ObjectiveRegistry<T> for dynamic objective dispatch; adapted to OSS Selection.item API; parking_lot dep added to khive-fold).

Tests: ~627 across the new code; cargo check --workspace clean.

2. Open-core scaffolds for pack-comm / channel / calendar / skills

Doc-comment-only scaffolds; impl is tomorrow's work. Strategy locked in a separate decision record (local working note, not in this PR).

Crate	Role
khive-pack-comm	Communication verb pack (declares note_kind=message)
khive-pack-skills	Skills verb pack (agent-discoverable directives)
khive-channel	ChannelHandler trait + envelope types
khive-channel-gmail	Gmail reference impl
khive-channel-macos-mail	Mail.app via AppleScript / MailKit (local-first)
khive-channel-macos-imessage	Messages + iMessage via chat.db
khive-calendar	CalendarHandler trait + event envelope types
khive-calendar-google	Google Calendar reference impl

Preserved AppleScript reference impls (mail_bridge.applescript, cal_bridge.applescript, test_mail_sync.sh) live under the respective crate's docs/reference/ for tomorrow's wiring pass.

3. Workspace update

crates/Cargo.toml registers the 12 new crates.

Suggested PR split for tomorrow

Each of these can land as its own PR with focused review:

1. khive-fold registry port — adds ObjectiveRegistry<T> + parking_lot dep. Tiny, lowest-risk first.
2. Retrieval port (4 crates) — khive-hnsw + khive-bm25 + khive-fusion + khive-retrieval. Largest. Could optionally split further by crate.
3. Channel surface — khive-channel + khive-pack-comm. Trait + pack that consumes it.
4. Channel reference impls — khive-channel-gmail + khive-channel-macos-mail + khive-channel-macos-imessage. Three impls of the same trait; could be one PR or three.
5. Calendar surface — khive-calendar + khive-calendar-google. Mirrors the channel pattern.
6. Skills pack — khive-pack-skills. Smallest scaffold, independent.

Test plan

• cargo check --workspace — verified clean locally before push
• cargo test --workspace for retrieval crates — verified ~627 tests pass locally
• Review trait surfaces in tomorrow's session before any of the scaffolds get implementation
• Confirm naming + pack vocabulary (note_kind=message, edge endpoint rules) before any pack-comm impl

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