channel-awareness: serve raw_window+digest from channel-memory

[mostlydev]

Motivation

Once channel-memory stores source messages and claw-wall pushes ingest, channel-awareness can graduate from raw-only context to raw_window+digest: recent raw messages plus compact older digest blocks with exact source provenance.

Depends on #265 and #266.

Scope

• Add claw-wall digest lookup from the /channel-awareness serving path.
• Keep the hot path LLM-free; /digest lookup must return already-processed blocks or fail open.
• Emit provider-visible headers with context_kind=raw_window+digest, digest status, digest age, source coverage, gaps, raw bytes, and digest bytes.
• Render raw recent messages with stable source handles and render digest blocks with source_channel plus source_messages provenance.
• Preserve exact retrieval through existing channel retrieval tools using channel id plus message ids.
• Update cllama/channel telemetry so channel_context_op distinguishes raw-only, digest, stale, unavailable, deterministic-only, and coverage-gap states.
• Track digest bytes separately from raw bytes in feed-budget accounting.

Out of scope

• Building the channel-memory storage adapter.
• Wiring claw-wall live push ingest.
• Async LLM digest generation; this issue can use deterministic digest blocks only.
• Release pin, changelog, or nav changes.

Acceptance

• Unit tests cover raw-only fallback, digest-ok, digest-stale, digest-unavailable, and coverage-gap rendering.
• Retrieval tests prove source provenance from a digest block round-trips to exact source messages.
• Telemetry tests prove digest status/coverage fields are emitted in channel_context_op.
• A spike test captures provider-visible raw_window+digest text and verifies meaningful byte reduction versus the raw-only path using a sanitized fixture.
• Public docs and examples stay deployment-agnostic.

Refs #262
Refs #263

[mostlydev]

Implementation notes carried from PR #270 review:

• The claw-wall: push channel messages into channel-memory #266 ingest source is first-sighting only. Treat live edit/delete freshness as unavailable unless a later gateway-event source supplies supersession/tombstone events. Digest status and staleness semantics should be honest about that boundary.
• claw-wall: push channel messages into channel-memory #266 coverage is split between compose-wiring unit tests and a Docker fake-Discord/fake-channel-memory spike that passes env directly. channel-awareness: serve raw_window+digest from channel-memory #267 should close the generated-compose seam with a real claw up pod where claw-wall and channel-memory are wired through the generated compose file.
• Real Discord/actual-pod validation belongs here because raw_window+digest is the first slice where the Plan + ADR for channel-memory capability and digest-backed channel-awareness (issue #232 Phase 2) #262 payoff is provider-visible to a live agent.

Refs #262 #266 #268