feat(planctl): context-window token awareness — core (parent 1.0)
- TokenCtx + Classify + formatTokenCount (R2.2, R3.1-3.5, R4.4)
- ReadTokenCtx orchestrator: env > PID walk > transcript parse (R1.1-1.6, R2.1-2.6)
- parseLastUsage: 10MB scanner, JSONL last-assistant-wins, zero-usage qualifies (R2.1-2.3)
- parsePIDFile: strict two-line layout; rejects partial/corrupted writes (R6.2-6.3)
- resolveViaPIDWalk: 8-hop ancestor walk, liveness + start-stamp check (R1.2, R6.1, R6.3)
- proc_darwin.go (x/sys/unix kinfo_proc) + proc_linux.go (/proc/stat field 22)
- parseStatStartTime: platform-agnostic, handles comm with parens/spaces
Parent 1.0 from dev/plans/26174-planctl-context-tokens/tasks.md
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