ln-401-task-executor

Paths: File paths (references/, ../ln-*) are relative to this skill directory.

Implementation Task Executor

Type: L3 Worker

Executes a single implementation (or refactor) task from Todo to To Review using the task description and linked guides.

Purpose & Scope

• Handle one selected task only; never touch other tasks.
• Follow task Technical Approach/plan/AC; apply KISS/YAGNI and guide patterns.
• Update tracker/kanban for this task: Todo -> In Progress -> To Review.
• Run typecheck/lint; update docs/tests/config per task instructions.
• Not for test tasks (label "tests" goes to ln-404-test-executor).

Hex MCP acceleration (if available): Use narrow inspect_path(path=<relevant dir>) and outline(file_path) before reading large code files; avoid repo-root wildcard inventories unless you intentionally need one. Use grep_search(output_mode="summary") first for search/discovery, then escalate to output_mode="content", edit_ready=true only when you need canonical hunks for follow-up edits; use allow_large_output=true only as an explicit last resort. Use read_file() in discovery mode for structure and targeted ranges; when you need revision and checksums for a follow-up edit, refresh that file with read_file(edit_ready=true, verbosity="full") before edit_file(). For edits to existing code, run index_project(path=project_root) once and use analyze_edit_region(...) before non-trivial edits. After edits: edit_file(base_revision=rev) -> verify(checksums). Before handoff: changes() to review diff.

Inputs

| Input | Required | Source | Description | |-------|----------|--------|-------------| | taskId | Yes | args, parent Story, kanban, user | Task to execute |

Resolution: Task Resolution Chain. Status filter: Todo

Task Storage Mode

MANDATORY READ: Load references/environment_state_contract.md, references/storage_mode_detection.md, references/tracker_provider_contract.md, references/provider_file.md, and references/input_resolution_pattern.md

Extract: task_provider = Task Management → Provider (linear | github | file). Operations stay provider-agnostic in this skill — see references/tracker_provider_contract.md for the canonical operation set and provider_*.md for transport binding.

Tool policy: follow host AGENTS.md MCP preferences; load references/mcp_tool_preferences.md and references/mcp_integration_patterns.md only when host policy is absent or MCP behavior is unclear. — use hex-line MCP for code files when available and hex-graph for semantic edit-risk questions.

Mode Detection

Detect operating mode at startup:

Plan Mode Active:

• Steps 1-2: Load task context (read-only, OK in plan mode)
• Generate EXECUTION PLAN (files to create/modify, approach) → write to plan file
• Call ExitPlanMode → STOP. Do NOT implement.
• Steps 3-6: After approval → execute implementation

Normal Mode:

• Steps 1-6: Standard workflow without stopping

Progress Tracking with TodoWrite

When operating in any mode, skill MUST create detailed todo checklist tracking ALL steps.

Rules:

1. Create todos IMMEDIATELY before Step 1
2. Each workflow step = separate todo item; implementation step gets sub-items
3. Mark in_progress before starting step, completed after finishing

Todo Template (10 items):

Step 1: Resolve taskId
  - Resolve via args / Story context / kanban / AskUserQuestion (Todo filter)

Step 2: Load Context
  - Fetch full task description + linked guides/manuals/ADRs

Step 2b: Goal Articulation Gate
  - Complete 4 questions from references/goal_articulation_gate.md (<=25 tokens each)

Step 2c: Implementation Blueprint
  - From task "Affected Components": extract file paths (Glob/Grep or narrow `inspect_path(path=<component dir>)` to find actual paths)
  - Read each file (or key sections) to understand current structure
  - IF modifying existing code in supported languages: `index_project(path=project_root)` once, then use path-scoped `find_symbols` / `inspect_symbol` for exact symbol identity and `analyze_edit_region` before editing non-trivial ranges
  - IF `find_symbols` returns `partial ... truncated=1` or a broad candidate set: refine to `name + file` or `workspace_qualified_name` before planning from it
  - Output:
    ## Implementation Blueprint: {taskId}
    **Files to create:** [list with brief purpose]
    **Files to modify:** [list with what changes]
    **Change order (dependencies first):**
    1. {file} — {what and why first}
    2. {file} — {depends on step 1}
    **Risks:** {shared files with parallel tasks, if any}
  - Scope: ONLY files of this task. Do not analyze other tasks.

  - **Checkpoint:** Emit PHASE_3 checkpoint with structured `blueprint` payload:
    `{ "blueprint": { "change_order": [{ "file": "...", "action": "create|modify", "reason": "..." }] } }`
    Guard blocks PHASE_4 if blueprint is missing from the checkpoint.

Step 3: Start Work
  - Set task to In Progress, update kanban

Step 4: Implement
  - 4a Pattern Reuse: IF creating new file/utility, Grep src/ for existing similar patterns
    (error handlers, validators, HTTP wrappers, config loaders). Reuse if found.
  - 4b Follow task plan/AC, apply KISS/YAGNI
  - 4c Architecture Guard: IF creating service function: (1) 3+ side-effect categories in **leaf** function → split (EXCEPT orchestrator functions that delegate sequentially — these are expected to have 3+ categories);
    (2) get_*/find_*/check_* naming → verify no hidden writes; (3) 3+ service imports in **leaf** function → flatten (orchestrator imports are expected)
    (4) **Frontend Guard (conditional):** IF affected files include `.tsx/.vue/.svelte/.html/.css` → **MANDATORY READ:** Load `references/frontend_design_guide.md`. Load project's design_guidelines.md if exists (design tokens source of truth). Verify: one composition per viewport; max 2 typefaces + 1 accent color; cards only when interaction requires; motion max 2-3 purposeful; WCAG 2.1 AA contrast (4.5:1 text, 3:1 UI elements)
  - Update docs and existing tests if impacted
  - Execute verify: methods from task AC (test/command/inspect)

Step 5: Quality
  - Run typecheck and lint (or project equivalents)
  - 5b Blueprint Completion: compare actual changes to blueprint; emit blueprint_status in PHASE_6 checkpoint

Step 6: Finish
  - Set task to To Review, update kanban
  - Add summary comment (changes, tests, docs)

Workflow (concise)

1) Resolve taskId: Run Task Resolution Chain per guide (status filter: [Todo]). 2) Load context: Fetch full task description via the configured tracker provider (getTask); read linked guides/manuals/ADRs/research; auto-discover team/config if needed. 2b) Goal gate: MANDATORY READ: Load references/goal_articulation_gate.md — Complete the 4-question gate (<=25 tokens each). State REAL GOAL (deliverable as subject), DONE LOOKS LIKE, NOT THE GOAL, INVARIANTS & HIDDEN CONSTRAINTS. 2c) Implementation Blueprint: From task "Affected Components", find actual file paths via Glob/Grep or narrow inspect_path(path=<component dir>). Read key sections of each file. If task changes existing code in supported languages, build graph context once (index_project) and use path-scoped find_symbols / inspect_symbol for exact symbol identity plus analyze_edit_region before editing non-trivial ranges. If symbol discovery is truncated, refine to name + file or workspace_qualified_name before planning from it. Output structured plan: files to create/modify, change order (dependencies first), risks (shared files with parallel tasks, external callers, public API surfaces). Scope: this task only. 3) Start work: Update this task to In Progress via the configured tracker provider (updateStatus); move it in kanban (keep Epic/Story indent). 4) Implement (with verification loop): Before writing new utilities/handlers, Grep src/ for existing patterns (error handling, validation, c