feat(agents): add low-friction decision prompts and /handoff exception

Bridged from Codex Game Studios commits 687320f and 2eae58d.

- Adds 'Low-Friction Decision Prompts' section: numbered options with one
  (Recommended), a. yes / b. no shortcuts for confirmations, no filler options.
- Adds /handoff exception to Collaboration Boundary: explicit /handoff
  invocation authorizes the declared handoff workflow (continuity writes,
  path-scoped staging, commit, push) without a second approval. Narrowly
  scoped - no source edits, branch switching, force-push, or --no-verify.
- Updates Continuity Epilogue point 3 to list viable actions.

Adapted Codex -> OpenCode: $handoff -> /handoff.

Author: Cipher-85

AGENTS.md

@@ -71,10 +71,35 @@ Question -> Options -> Decision -> Draft -> Approval.
   tools.
 - Agents must show drafts or summaries before requesting approval.
 - Multi-file changes require explicit approval for the full changeset.
+- `/handoff` exception: explicit invocation of the OpenCode-native `/handoff`
+  skill counts as user approval for that skill's declared handoff workflow only:
+  update `production/session-handoff.md`, `production/session-archive.md`, and
+  `production/session-state/active.md`; stage relevant uncommitted changes by
+  path; create the standard handoff commit; and push the current branch.
+- The `/handoff` exception does not authorize design/game-feel/balance
+  decisions, new source edits outside the continuity files, writes to undeclared
+  files, branch switching, force-pushes, or `--no-verify` / amend workarounds.
 - No commits without user instruction.
 
 See `docs/COLLABORATIVE-DESIGN-PRINCIPLE.md` for full protocol and examples.
 
+## Low-Friction Decision Prompts
+
+OpenCode surfaces may not always provide a clickable choice UI. When handing
+control back to the user, make the reply easy to answer with a short token.
+
+- For multiple viable choices, list all real options, usually 3-5 when available
+  and fewer when fewer are viable. Do not invent filler options.
+- Use numbered options for multi-choice prompts. Mark exactly one option
+  `(Recommended)`.
+- For yes/no confirmations, include explicit letter shortcuts:
+  - `a. yes`
+  - `b. no`
+- Keep each option label short. Put reasoning in one brief sentence before the
+  options or after each option only when needed.
+- Never end with an unstructured "what do you want to do?" when a small viable
+  choice set is possible.
+
 ## Verification Integrity
 
 - Never claim a build, test, lint, smoke check, or playtest passed unless it ran
@@ -160,8 +185,8 @@ After each discrete work unit, apply this mentally or run `/studio-next`:
 
 1. Summarize what was completed.
 2. Surface owed verification.
-3. Recommend the single best next action from handoff, session, sprint, stage,
-   workflow, and slice state.
+3. List the viable next actions from handoff, session, sprint, stage, workflow,
+   and slice state, with one clearly marked `(Recommended)`.
 4. Suggest `/handoff` when session state should be preserved.
 
 Read `.opencode/docs/session-continuity.md` and