Why: Old tool results were filling the window, compaction could split a tool group or commit a stale summary, and reminders arrived as extra user messages.
Evidence: Compaction retries a conflict and opens the circuit after three failures; clearing keeps the last five tool results; a stale file write is rejected; RPC reports started, queued, or handled.
Impact: Requests over the context window replace older tool results with a placeholder. Rewriting an existing file now requires a read in the same run. Subagent text over 32000 characters is capped.
Refs: feature/context-engineering
Co-authored-by: Cursor <cursoragent@cursor.com>
Why: token budget let the current tool batch run, compaction could split a tool pair or race an append, writes were not crash-atomic, and several MCP and session edges only existed as comments.
Evidence: GOWORK=off go test -count=1 -race ./runtime/ ./runtime/llm/ ./runtime/session/ ./runtime/tools/ ./runtime/mcp/ ./adapters/native/ ./adapters/intentgate/ passed, including the TestR2* cases for budget, replacement, cancel, compaction, SSE, UTF-8, schema, MCP retry, session terminate, poison reload, and registry reload.
Impact: over-budget tool calls are skipped and paired; Stop.Replacement is appended to the session; the intent gate can follow Registry.Reload.
Refs: N5, N6, N7, N8, N9, N11, N12, N15, N16, N17, N18, N19, N21, I9
Co-authored-by: Cursor <cursoragent@cursor.com>
Why: Linear transcripts cannot fork, and compaction rewrote history, so resume and branch navigation had nothing to point at.
Evidence: go test -count=1 ./runtime/session/
Impact: Load still returns the model-visible path, including old one-message-per-line files. Compaction appends a summary entry instead of truncating the file.
Refs: feature/pi-headless N1
Co-authored-by: Cursor <cursoragent@cursor.com>
Why: long multi-turn executions grow the JSONL transcript until they
hit provider context limits (parity-matrix #11), and a crashed append
left a partial line that made the whole session unloadable
(parity-matrix #12 resume semantics).
Evidence: go vet ./... clean; go test ./... 13 packages ok. Session
cases: crash-residue tail skipped while mid-file corruption still
errors, Stats line/byte counts, meta sidecar roundtrip (missing meta
nil), Compact rewriting system+summary+keepLastN atomically with no
tmp residue, no-op on short transcripts, summarizer error leaving the
file untouched. Adapter case: threshold-triggered compaction runs
before the loop and the summary marker reaches both the transcript
and the model's context.
Impact: session gains Stats/SaveMeta/ReadMeta/Compact; native.Options
gains Compact *CompactConfig (default summarizer is one tool-less
stream call; compaction failure logs and continues - optimization,
never a silent failure); session meta sidecar records model/scope/
exec id per execution.
Refs: docs/parity-matrix.md #11/#12 (Batch3 scope).
weichenandCursor