feat(skills): ship handoff as a bundled default skill (generation 9)

The handoff skill (baton-pass: write a compact decision-ready handoff,
persist it, make the context disposable for the next session) becomes a
first-party default skill so operate-mode operations can continue across
sessions. Bundled at generation 9: HANDOFF_BODY include_str, bundle
entry, canonical list via BUNDLED_SKILLS, and a v8->v9 version-bump
test mirroring the v5 pattern.

Verified: skills::system tests 21/21.

crates/tui/assets/skills/handoff/SKILL.md

@@ -0,0 +1,88 @@
+---
+name: handoff
+description: >-
+  Write a compact, decision-ready handoff so the next session (or the user)
+  can continue without reconstructing the current one. Use when the session
+  is ending, context is running low, the user asks for a handoff / "pass the
+  baton" / "hand off", or a long-running operation needs a durable state
+  checkpoint.
+---
+
+# Handoff
+
+> Write a compact, decision-ready handoff so the next session (or the user)
+> can continue without reconstructing the current one. Use when the session is
+> ending, context is running low, the user asks for a handoff / "pass the
+> baton" / "hand off", or a long-running operation needs a durable state
+> checkpoint. The goal: the durable artifact survives, the context does not
+> need to.
+
+Invocation: `model+user`
+
+## When to use
+
+- The user says "handoff", "hand off", "pass the baton", "takeover prompt",
+  "write me a handoff", or the session is about to end / compact.
+- A long operation (multi-turn, multi-workstream) has state that must survive
+  context loss: commits, branches, PRs, CI, blockers, decisions.
+- You are switching to a fresh session and want the new session to start from
+  evidence instead of reconstructing the old one.
+
+## What to do
+
+1. **Gather the truth from tools, not memory.** Run/collect:
+   - `git branch --show-current`, `git status --short`, `git log --oneline
+     origin/<default>..HEAD` (what is local-only), `git log --oneline -5`
+     (recent context).
+   - Live remote state where relevant (`gh pr list --state open`,
+     `gh pr checks <n>`, `gh run list`) — only what the user's operation
+     actually depends on; do not pad the handoff with a full GitHub dump.
+   - Any in-flight work: dirty files, uncommitted slices, partial worktrees,
+     running background jobs/workers, queued CI.
+2. **Write a compact markdown handoff** (aim under ~60 lines; the user may
+   also ask for a "short text-only" variant — then aim under ~15 lines):
+
+   ```markdown
+   # Handoff — <operation/session name> — <date>
+   - **State:** <one-line: what is done vs in-flight vs blocked>
+   - **Landed/committed:** <exact SHAs + one-line what>
+   - **Branches/PRs:** <names + states; which are ours vs community>
+   - **CI:** <what is green, what is waiting, what is broken>
+   - **Blockers:** <exact blocker + what would unblock>
+   - **Decisions made:** <the WHY that a fresh session must not re-litigate>
+   - **Next step:** <the single next action, one line>
+   - **Continuation records:** <pointers to partial work that must be
+     preserved (worktrees, uncommitted files, receipts)>
+   ```
+
+3. **Persist it.** Write the handoff to the agreed location:
+   - If the workspace has an ops/notes convention (e.g. `codewhale-ops/notes/`
+     with a living handoff file), update the living handoff's dated facts and
+     snapshot, or create `<topic>-handoff-<date>.md` next to it.
+   - Otherwise write to the repo root as `HANDOFF.md` or
+     `docs/handoff/<topic>-<date>.md`; never overwrite someone else's
+     uncommitted handoff without reading it first.
+4. **Clear the way for the new session ("clears context").** A skill cannot
+   delete the current context, but it can make the context disposable:
+   - Ensure nothing is left only in memory: dirty work is either committed
+     (WIP is fine with a real body), stashed with a note, or recorded in the
+     handoff with its exact location.
+   - Kill or record background work that would outlive the session
+     (background jobs, sub-agents) — record what is still running and its
+     task id.
+   - Close with the one-line "next step" so the fresh session has an
+     unambiguous first action.
+5. **Deliver.** Give the user the compact handoff text in your reply
+   (the persisted file is the durable copy; the reply is the readable one).
+
+## Constraints
+
+- Facts only from tool output; never invent SHAs, check states, or blockers.
+- Keep claims narrower than evidence: distinguish landed/committed, verified
+  locally, CI-verified, and pending.
+- Preserve other people's uncommitted work: read before touching, archive
+  before overwriting.
+- The handoff is orientation, not law: tell the next session to refresh
+  live state before acting on it.
+- If the user asks for a "short text-only" handoff, give exactly that in the
+  reply and skip the full markdown file unless asked.

crates/tui/src/skills/system.rs

@@ -10,7 +10,9 @@ use std::path::Path;
 /// Generation 7 adds the explicit-only `help` router (#4698 parity slice).
 /// Generation 8 adds the explicit-only `contributor-onboarding` path
 /// requested by @JayBeest (#4227).
-const BUNDLED_SKILL_VERSION: &str = "8";
+/// Generation 9 adds the `handoff` workflow skill (baton-pass for
+/// continuous operate-mode operations).
+const BUNDLED_SKILL_VERSION: &str = "9";
 
 // ── system & extension (meta) ───────────────────────────────────────────────
 const SKILL_CREATOR_BODY: &str = include_str!("../../assets/skills/skill-creator/SKILL.md");
@@ -22,6 +24,7 @@ const FLEET_MANAGER_BODY: &str = include_str!("../../assets/skills/fleet-manager
 const HELP_BODY: &str = include_str!("../../assets/skills/help/SKILL.md");
 
 // ── end-user workflows ──────────────────────────────────────────────────────
+const HANDOFF_BODY: &str = include_str!("../../assets/skills/handoff/SKILL.md");
 const BEST_OF_N_BODY: &str = include_str!("../../assets/skills/best-of-n/SKILL.md");
 const INTERVIEW_BODY: &str = include_str!("../../assets/skills/interview/SKILL.md");
 const PLAN_BODY: &str = include_str!("../../assets/skills/plan/SKILL.md");
@@ -104,6 +107,11 @@ const BUNDLED_SKILLS: &[BundledSkill] = &[
         introduced_in: 7,
     },
     // End-user workflows
+    BundledSkill {
+        name: "handoff",
+        body: HANDOFF_BODY,
+        introduced_in: 9,
+    },
     BundledSkill {
         name: "best-of-n",
         body: BEST_OF_N_BODY,
@@ -551,7 +559,7 @@ mod tests {
             .find(|skill| skill.name == "contributor-onboarding")
             .expect("contributor-onboarding must be bundled");
         assert_eq!(skill.introduced_in, 8);
-        assert_eq!(BUNDLED_SKILL_VERSION, "8");
+        assert_eq!(BUNDLED_SKILL_VERSION, "9");
 
         let body = skill.body;
         assert!(body.contains("invocation: explicit-only"));
@@ -815,6 +823,24 @@ mod tests {
         assert_eq!(ver.trim(), BUNDLED_SKILL_VERSION);
     }
 
+    #[test]
+    fn version_bump_from_v8_adds_handoff_without_recreating_deleted_skills() {
+        let tmp = TempDir::new().unwrap();
+        fs::write(marker_file(&tmp), "8").unwrap();
+
+        install_system_skills(tmp.path()).unwrap();
+
+        assert!(skill_file(&tmp, "handoff").is_file());
+        assert!(
+            !skill_file(&tmp, "delegate").exists(),
+            "an intentionally absent older skill must stay absent"
+        );
+        assert_eq!(
+            fs::read_to_string(marker_file(&tmp)).unwrap().trim(),
+            BUNDLED_SKILL_VERSION
+        );
+    }
+
     #[test]
     fn version_bump_from_v5_adds_best_of_n_without_recreating_deleted_skills() {
         let tmp = TempDir::new().unwrap();