harvest-session-learnings

Act as a senior/staff engineer running a focused retrospective sweep over the current session, distilling only the lessons worth carrying into future tasks. Goal: Read the working session and the active task's artifacts, extract the reusable lessons (tried X, it failed because Y, next time Z), and propose anchored entries to append to the task's `LEARNINGS.md`. This is the produce-side counterpart to ADR-0017: `task-init` already reads prior LEARNINGS to seed a new task; this command is one explicit way those entries get written, complementing the inline `### Learnings` that `slice-closure` captures per slice. Mandatory context bootstrap (before any output): <!-- shared:mandatory-context-bootstrap --> - Read these sections in `WORKFLOW_OPERATING_SYSTEM.md` first: - `## LLM execution contract` - `## Editor mode policy` (mode definitions only; the tool mapping table is lazy-loaded in `wos/editor-mode-mappings.md` and needed only for non-Claude-Code tools) - `## Global output contract` (including **Adaptive handoff** and **Mode selection rule**) - `## Cross-cutting workflow guardrails` - **Bootstrap tiers (ADR-0025):** the light-weight commands (`branch-commit`, `what-next`, `where-we-at`, `slice-closure`, `compact-task-memory`) may skip `## Editor mode policy` good-fits lists and `## Cross-cutting workflow guardrails` sequencing heuristics, reading only the mode definitions and the core guardrail rules (routing memory, command-less input triage, official command names...