Owner report (OpenRouter logs, 2026-10-05): the post-compaction request
arrived with NO system prompt and NO tool definitions — everything
before the cut replaced by the compaction message.
Root cause: pi-agent-core's Agent seeds a SystemMessage carrying the
system prompt AND the tool declarations at state.messages[0]
(createInitialSystemMessage — 'messages declare the provider-visible
loadout'). The record never persists it (ui-stream's settleWith filters
the role), but convertToLlm DOES receive it — and the cut projection
sliced from firstKeptMessageId, dropping [0] from the wire: no prompt,
no tools.
Fix (pi's own law — verified against pi-agent-core + pi's coding-agent):
the projection now carries the leading system message through AHEAD of
the compaction head, exactly as pi's prepareRequest re-applies
context.systemPrompt + context.tools around its compaction projection.
The cut slices the RECORD's history; the chrome is never compactable
payload. Loop start skips [0] when chrome is present (no duplicate);
record-path callers are unchanged.
Pinned: chrome-first-through-cut, exactly-once without a cut,
record-path head-first.
- src/server/compaction.ts: ensureCompacted (the turn-start gate — awaits
in-flight compaction, compacts synchronously when still over threshold),
kickCompaction (the settle kick — summary starts inside the learner's
reading/answering pause; question/problem poses end runs so the pause is
always a between-runs window), registry mutex on globalThis, anti-churn
guard (empty-span skip), summary via the zero-tool one-shot sub-agent
seam on the session's OWN engine (owner ruling), usage to the turns log
keyed by the marker, record-changed + compaction-changed events
- chat-handler: the gate rides with the BYOK/key gates (before appends,
beginTurn; record re-read after); the kick at the onFinish tail
(re-resolves engine fresh; silent no-op when engineless)
- events: compaction-changed {chatId, running} — running=true is the
client send-gate signal
- settings: compaction.thresholdTokens (factory 150k, floor 32k,
clamp-never-reject) resolved concrete in EffectiveSettings
- effective threshold = min(setting, contextWindow − 16k) over the live
catalog index
- overflow recovery needs no special path: the next turn's gate compacts
- 8 service pins (mutex, events order, chained spans, failure re-arm)
amosblomqvist