Add transport-neutral conversation materialization #224

Feature description

Add a transport-neutral library that converts closed conversation windows into immutable source documents.

Motivation

Conversation sources need stable evidence identifiers, deterministic document boundaries, content hashes, and replay-safe resume state. These rules do not belong to one transport, database, scheduler, or model provider.

The library must preserve caller-supplied source, speaker, authority, time, and evidence identifiers. It must fail closed when a turn cannot fit one complete rendered document.

Proposed solution

Add a small conversation package that provides:

• Typed conversation turns and closed windows
• Deterministic text cleaning
• Explicit optional truncation with an omitted-middle digest
• Exact duplicate handling
• Turn-boundary splitting
• Final rendered-document size checks
• Closed-window fingerprints
• Content-addressed manifests
• Replay-safe resume state
• Recovery splitting for uncompiled documents
• Oldest-first bounded compile selection
• Compile-budget checks
• Optional compile receipts
• Verified claim application through the temporal-claims API

Scope boundaries

The caller controls source filters, window boundaries, privacy filters, credentials, and scheduler limits.

The change must not add:

• Database queries
• Transport-specific rules
• Live input
• Scheduler wiring
• Model calls
• Private source content
• Ingest-bundle plugin registration

This feature does not depend on PR #179. A future PR #179 adapter can call the conversation materializer.

The implementation depends on the temporal-claims API in PR #223.

Validation

Use deterministic synthetic tests. Require full tests, Ruff, format checks, Mypy, file-size checks, privacy scans, and package builds.