MemoryService read-path: reconstruct turn-document from split metadata when the stored copy is dropped (#14193 slice-3)

Context

Slice-3 of the #14193 field↔document de-dup (part of #14079 bloat). Slice-1 (#14202, composeTurnDocumentText) + slice-2 (#14206/#14207, write-path single-source) are in. This is the read-path: MemoryService's two collection.get(['documents']) neighbor-recall paths must reconstruct the turn-document from split metadata when the redundant stored document has been dropped (so the slice-4 migration is safe), gated on the turn-vs-summary discriminator.

Change

• New pure resolveTurnDocumentForRead({documents, metadata}) in turnDocumentText.mjs (read-side, beside the write-side composeTurnDocumentText): prefers the stored document (byte-exact, behavior-preserving for existing records); else reconstructs via composeTurnDocumentText ONLY for turns (metadata.type === 'agent-interaction'); a summary (distinct shape) is never reconstructed → its stored document or null. Single-sources the discriminator so every read-path shares it.
• The two MemoryService neighbor-recall reads (strategic content, episodic episodicContext) call it; the episodic read adds metadatas to its include.

Acceptance Criteria

• Both neighbor-recall reads reconstruct turn-documents from metadata when the stored document is absent; stored document still wins when present (behavior-preserving).
• Summaries (non-agent-interaction) are NEVER reconstructed via the turn template.
• resolveTurnDocumentForRead is pure + total (unit-tested: stored-wins, dropped-doc reconstruct across [null]/[]/undefined, summary-never-reconstruct, null-safety).

Links

Part of #14193 (de-dup) · #14079 (bloat). Stacked on #14207 (slice-2) + #14202 (slice-1). I co-drive slice-4 (the migration) with @neo-opus-ada next.

Authored by Grace (Claude Opus 4.8, Claude Code). Session 090a68e6-1a28-4b20-a5fd-842ebac3e729.