feat(skills/code-agent): ticket-driven mode (plan-first carve-out) (closes #73)

[initializ-mk]

Summary

Single-file SKILL.md update to the existing code-agent skill. No tool signatures, scripts, or scaffold templates change — the entire diff is in the system-prompt body. The EXECUTE mantra is preserved for direct user requests; a planning carve-out is added for ticket-driven mode.

Closes #73.

What changed

forge-skills/local/embedded/code-agent/SKILL.md (+67 / −5):

1. Frontmatter

Added ticket-driven to tags. Nothing else touched (bins, egress_domains, timeout_hint, denied_tools, etc. all preserved).

2. ABSOLUTE RULES

Rule	Status
1	Modified — "tool calls OR a structured plan presentation"
2	Modified — narration-without-action forbidden; ticket-driven exception explicitly allows code_plan_create + plan presentation
3	Modified — confirmation EXCEPTION for complexity: \"high\" or non-empty risks after code_plan_create
4	Unchanged verbatim
5	Modified — direct requests still one-shot; ticket-driven follows plan → present → confirm if needed → write → test → commit → push → PR
6	Unchanged verbatim
7	Unchanged verbatim

3. New "Ticket-Driven Mode" section

Placed exactly where the issue specified — between Iteration Rules and Full-Stack Architecture. Contents:

• Trigger — three signals: conversation began with linear_*/github_get_issue, ticket-id pattern in user message, pasted ticket structure
• Required sequence (8 steps) — including the open_questions-cannot-resolve → comment-and-stop rule
• Plan adherence — plan is a contract; regenerate rather than drift; writing files outside the plan ⇒ stop
• What this does NOT change — direct requests stay one-shot; framework conventions / scaffold rules / tool signatures all preserved

4. New "Ticket-Driven Implementation" sub-flow

Added as the fourth sub-flow under One-Shot Workflow (after New Project / Existing Codebase / Modify Existing). 12-step canonical sequence from linear_get_issue through linear_add_comment, with an explicit "Do NOT call code_agent_scaffold" closer.

5. Tool Reference table

Added one pointer row at the top for code_plan_create flagged as living in the sibling code-plan skill, plus a clarifying note below the table: "In ticket-driven mode the code-plan skill is a hard prerequisite." No ## Tool: code_plan_* heading added to this file — the pointer is in the reference table only, preserving the single-skill ownership of each tool.

6. Safety bullet

Before: "Do not create git commits unless explicitly asked."
After: "Do not create git commits unless the request requires them. Direct one-shot scaffolds typically do not commit. Ticket-driven flows always commit and PR — that's the whole point."

Resolves the contradiction with the new flow.

Verification

• grep -c '^## Ticket-Driven Mode$' SKILL.md → 1 (exactly one new section heading)
• grep -c '^### Ticket-Driven Implementation$' SKILL.md → 1
• All 5 ## Tool: code_agent_* headings preserved (scaffold, write, read, edit, run)
• Zero ## Tool: code_plan_* headings — pointer is table-only, no scope leakage
• go test ./forge-skills/... — all green (15 skills, TestEmbeddedRegistry_LoadContent still finds ## Tool: headings)
• golangci-lint run ./forge-skills/... — 0 issues
• No script changes → shellcheck not run (no surface)
• Manual: forge build against a test agent with code-agent enabled produces a system prompt containing "Ticket-Driven Mode" — jq '.system_prompt' .forge-output/agent-spec.json | grep -c 'Ticket-Driven Mode' → expected 1
• Manual: agent driven from Telegram with a Linear ticket triggers the plan-first flow; a direct "build me a todo app" request still scaffolds in one turn

Out of scope per #73

• No new tools in this skill
• No tool signature changes
• No mode parameter — mode is inferred from conversation context as documented
• No script touches, no framework template changes, no scaffold rule edits
• No "plan mode" toggle in forge.yaml
• No telemetry, no cross-skill state sharing
• No auto-classification of ticket-driven mode beyond the three documented signals

Prerequisite stack (all merged)

PR	Provides
#67 (linear)	linear_get_issue / linear_add_comment referenced in the required sequence
#69 (code-plan)	code_plan_create — hard prerequisite for ticket-driven mode
#71 (github update)	github_branch_name_from_ticket + ticket-aware github_create_pr referenced in the 12-step sub-flow

Together with this PR, the canonical ticket → plan → branch → write → test → commit → PR → comment flow is fully wired across the four skills.