Move checkpoint, index, trie, and read caches to git-cas pages

[flyingrobots]

Parent: #734
Blocked by: #735, #737, #738

Outcome

Checkpoint, bitmap/property index, trie, and repeated read storage use git-cas bundles/pages and git-cas-owned residency policy.

Scope

• Replace manual checkpoint/index blob and tree assembly.
• Move GitTrieStoreAdapter and PageCache behavior behind git-cas page storage.
• Remove WARP LRU caches from BitmapIndexReader, PropertyIndexReader, and TraversalContext.
• Preserve Roaring bitmap/index schemas and query semantics in WARP.
• Make checkpoint publication pin the same materialization bundle rather than copy a second state representation.
• Remove latent writeShards and pointer protocols.

Proof

• Individual pages/shards stream without opening unrelated members.
• Identical pages deduplicate.
• Checkpoint and live materialization share one immutable representation.
• Reader memory remains bounded.
• Related BitmapIndexBuilder/Reader/Streaming always change together (22x in 3 months) #375, PROTO_streaming-bitmap-index-builder-serialization-tail #387, and MaterializedViewService carries index verification concern #228 are closed or narrowed with evidence.

[coderabbitai]

🔗 Related PRs

#93 - Fix recursive tree OID read fanout and release v17.0.1 [merged]
#107 - Prepare v18.0.0 release metadata and final gates [merged]
#588 - Fix #377: Signal bitmap shard corruption [merged]
#708 - Fix live materialization state-cache hits [merged]
#726 - Move graph exports behind v19 public API boundary [merged]

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[flyingrobots]

Acceptance addendum: repeated bounded observations must warm-hit\n\nThe cache/materialization complaint is a release blocker, not optional optimization.\n\nRequired proof:\n- Repeating a blessed property and neighborhood Observer at the same coordinate reuses retained git-cas pages across Runtime reopen.\n- Warm reads open only the support/index/data pages required by the optic; they do not reconstruct complete ORSets or hydrate the whole chart.\n- Diagnostics expose hit/miss, handle, age, logical/physical size where available, pages opened, bytes streamed, and timing by phase.\n- Identical page content deduplicates through git-cas; no WARP LRU, page cache, mutable cache ref, or duplicate checkpoint representation remains.\n- Benchmarks gate on bounded pages/bytes and skipped reduction work, with wall-clock values reported but not used as brittle pass/fail ratios.