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
