handoff

Produce a self-contained context payload that lets a fresh agent continue this work without re-deriving or re-learning what this session already established. The argument is what the next session is for — use it to shape what's captured and what's left out. Capture what's hard-won — anything the new session would have to re-do otherwise. For each item that travels, carry the grounding with it, so the receiver inherits the working state rather than just the conclusion. *Examples (illustrative, not required):* a settled decision travels with the alternatives considered and why this won; a verified fact travels with how it was verified (file:line, command output, doc URL); an open thread travels with what would close it. If a particular handoff isn't structured around decisions, facts, or threads, capture whatever the goal requires — with its grounding. Reference other artifacts (PRDs, manifests, ADRs, issues, PRs, commits, diffs) by path or URL — don't restate their content. Shape is the agent's call. Section names, headings, prose-vs-lists, ordering — driven by the intent, not a template. Output to `~/.manifest-dev/handoffs/handoff-{timestamp}.md` (create the dir; `~` = `$HOME` / `%USERPROFILE%`) where `{timestamp}` is `YYYYMMDD-HHMMSS` in UTC — a durable home so handoffs survive OS temp cleanup between sessions. Fall back to a writable temp path only when the home directory isn't writable. If the argument is a path to a prior handoff, read it first and write a fresh doc r...