Why: the completion doc's N2 requires old tool results to become file
paths (ZCode compact pattern) and cache-friendly prefix rules; today the
micro-compactor only left a transcript pointer and nothing pinned prefix
stability. alignToolTail had no direct edge tests.
Evidence: GOWORK=off go vet + go test -count=1 ./... green; new
TestClearOldToolResultsSpillsToDisk / TestSpillResultSanitizesCallID /
TestAlignToolTailEdges / TestSystemTextDeterministicAcrossIdenticalBuilds;
legacy placeholder bytes unchanged when ResultsDir is empty
(TestClearOldToolResultsEmptyDirKeepsLegacyPlaceholder).
Impact: opt-in via Config.ResultsDir; the native adapter wires it to
<workDir>/.agentx/results. No behavior change for other hosts.
Refs: 2026-10-07-agent-stack-n2-plan WP1
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>
weichen
