Live compaction synthesis can leak raw analysis and summary XML into the feed

[Juliusolsson05]

Problem

During /compact, the feed can render the raw synthesis response as ordinary assistant markdown, including <analysis> / <summary> style content, instead of showing the live compaction placeholder.

Evidence

Bundle 2026-06-22T12-42-54-045-c973322e:

• feed-debug.jsonl: claude.compaction condition is visible/running.
• proxy-semantic.json.currentTurn.text starts with <analysis>.
• Semantic turn_started event has no isCompactionSynthesis.
• proxy-events.jsonl: request flow reports request_shape.compaction_synthesis:false.

Bundle 2026-06-14T14-02-05-796-a8ad1ebb:

• Same shape: semantic current turn text starts with <analysis>, text length around 15k, rendered as a normal semantic block.

Suspected Cause

The proxy compaction detector likely depends on a request signature that drifted. Because request shape explicitly reports compaction_synthesis:false, the adapter does not attach isCompactionSynthesis, and StreamingTurn renders the raw semantic text.

Related paths:

• packages/claude-code-headless/src/proxy/mitmAddon.py
• packages/claude-code-headless/src/proxy/ClaudeProxyAdapter.ts
• src/renderer/src/features/feed/ui/semantic/StreamingTurn.tsx

Expected

When any reliable signal says compaction is running, the feed should never paint raw synthesis XML. It should show the compaction placeholder until compact boundary/summary entries land.

[Juliusolsson05]

Linking this back to #172. This issue has a provider-detection side, but it is also an ownership failure: raw compaction synthesis text is allowed to render even while another signal says compaction is active.

The detector may still need a targeted fix, but the #172 single-owner feed model should prevent raw synthesis content from painting whenever a compaction owner is active. Re-test after #172 to separate renderer ownership leftovers from proxy/request-shape detection leftovers.