Implementer Skill

Thin wrapper that delegates general implementation to general-implementation-agent subagent.

IMPORTANT: This skill implements the skill-internal postflight pattern. After the subagent returns, this skill handles all postflight operations (status update, artifact linking, git commit) before returning. This eliminates the "continue" prompt issue between skill return and orchestrator.

Context References

Reference (do not load eagerly):

Path: .claude/context/formats/return-metadata-file.md - Metadata file schema
Path: .claude/context/patterns/postflight-control.md - Marker file protocol
Path: .claude/context/patterns/file-metadata-exchange.md - File I/O helpers
Path: .claude/context/patterns/jq-escaping-workarounds.md - jq escaping patterns (Issue #1132)

Note: This skill is a thin wrapper with internal postflight. Context is loaded by the delegated agent.

Trigger Conditions

This skill activates when:

Task type is "general", "meta", or "markdown"
/implement command is invoked
Plan exists and task is ready for implementation

Execution Flow

Stage 1: Input Validation

Validate required inputs:

task_number - Must be provided and exist in state.json
Task status must allow implementation (planned, implementing, partial)

# Lookup task
task_data=$(jq -r --argjson num "$task_number" \
  '.active_projects[] | select(.project_number == $num)' \
  specs/state.json)

# Validate exists
if [ -z "$task_data" ]; then
  return error "Task $task_number not found"
fi

# Extract fields
task_type=$(echo "$task_data" | jq -r '.task_type // "general"')
status=$(echo "$task_data" | jq -r '.status')
project_name=$(echo "$task_data" | jq -r '.project_name')
description=$(echo "$task_data" | jq -r '.description // ""')

# Validate status
if [ "$status" = "completed" ]; then
  return error "Task already completed"
fi

Stage 2: Preflight Status Update

Update task status to "implementing" BEFORE invoking subagent.

Run the centralized status update script, which atomically updates state.json, TODO.md (task entry + Task Order), and the plan file:

bash .claude/scripts/update-task-status.sh preflight "$task_number" implement "$session_id"

Note: The script handles all three updates (state.json status/timestamps/session_id, TODO.md [PLANNED] -> [IMPLEMENTING] in both task entry and Task Order, and plan file status -> [IMPLEMENTING]) in a single call. No additional Edit or jq operations are needed.

Stage 3: Create Postflight Marker

Create the marker file to prevent premature termination:

# Ensure task directory exists
padded_num=$(printf "%03d" "$task_number")
mkdir -p "specs/${padded_num}_${project_name}"

cat > "specs/${padded_num}_${project_name}/.postflight-pending" << EOF
{
  "session_id": "${session_id}",
  "skill": "skill-implementer",
  "task_number": ${task_number},
  "operation": "implement",
  "reason": "Postflight pending: status update, artifact linking, git commit",
  "created": "$(date -u +%Y-%m-%dT%H:%M:%SZ)",
  "stop_hook_active": false
}
EOF

Stage 3a: Calculate Artifact Number

Read next_artifact_number from state.json and use (current-1) since summary stays in the same round as research/plan:

# Read next_artifact_number from state.json
next_num=$(jq -r --argjson num "$task_number" \
  '.active_projects[] | select(.project_number == $num) | .next_artifact_number // 1' \
  specs/state.json)

# Implement uses (current - 1) to stay in the same round as research/plan
# If next_artifact_number is 1 (no research yet), use 1
if [ "$next_num" -le 1 ]; then
  artifact_number=1
else
  artifact_number=$((next_num - 1))
fi

# Fallback for legacy tasks: count existing summary artifacts
if [ "$next_num" = "null" ] || [ -z "$next_num" ]; then
  padded_num=$(printf "%03d" "$task_number")
  count=$(ls "specs/${padded_num}_${project_name}/summaries/"*[0-9][0-9]*.md 2>/dev/null | wc -l)
  artifact_number=$((count + 1))
fi

artifact_padded=$(printf "%02d" "$artifact_number")

Note: Implement does NOT increment next_artifact_number. Only research advances the sequence.

Stage 4a: Memory Retrieval (Auto)

Retrieve relevant memories from the memory system to inject into the delegation context.

Skip if: clean_flag is true in the delegation context (from --clean command flag).

# Check clean_flag
if [ "$clean_flag" != "true" ]; then
  memory_context=$(bash .claude/scripts/memory-retrieve.sh "$description" "$task_type" "" 2>/dev/null) || memory_context=""
fi

# memory_context will be empty string if:
# - clean_flag is true (skipped)
# - memory-index.json missing or empty
# - no keywords matched any entries
# - script exited with error

If memory_context is non-empty, it will be injected into the Stage 5 prompt alongside the format specification from Stage 4b. If empty, no memory block is injected.

Stage 4: Prepare Delegation Context

Prepare delegation context for the subagent:

{
  "session_id": "sess_{timestamp}_{random}",
  "delegation_depth": 1,
  "delegation_path": ["orchestrator", "implement", "skill-implementer"],
  "timeout": 7200,
  "task_context": {
    "task_number": N,
    "task_name": "{project_name}",
    "description": "{description}",
    "task_type": "{task_type}"
  },
  "artifact_number": "{artifact_number from Stage 3a}",
  "effort_flag": "{effort_flag from command, null if not set}",
  "model_flag": "{model_flag from command, null if not set}",
  "plan_path": "specs/{NNN}_{SLUG}/plans/MM_{short-slug}.md",
  "metadata_file_path": "specs/{NNN}_{SLUG}/.return-meta.json"
}

Note: The artifact_number field tells the agent which sequence number to use for artifact naming (e.g., 01, 02). Summary uses the same round number as the research and plan that preceded it.

Model/Effort Flags: If model_flag is set (haiku, sonnet, opus), pass it as the model parameter on the Task tool to override the agent's frontmatter default. If effort_flag is set (fast, hard), include it as prompt context for reasoning depth guidance.

CRITICAL: No Source Reading Before Delegation -- Between preparing the delegation context (Stage 4) and spawning the sub-agent (Stage 5), the lead skill MUST NOT read, grep, glob, or analyze source files. The plan file and state.json are the only files the lead reads. All codebase exploration (reading source files, grepping for patterns, using MCP tools) is the exclusive responsibility of the sub-agent after it is spawned.

Stage 4b: Read and Inject Format Specification

Read the summary format file and prepare it for injection into the subagent prompt. This ensures the subagent always has the full format specification in its context, regardless of whether it reads the file itself.

format_content=$(cat .claude/context/formats/summary-format.md)

The format content will be included as a delimited section in the Stage 5 prompt (see below).

Stage 5: Invoke Subagent

CRITICAL: You MUST use the Task tool to spawn the subagent.

Required Tool Invocation:

Tool: Task (NOT Skill)
Parameters:
  - subagent_type: "general-implementation-agent"
  - prompt: [Include task_context, delegation_context, plan_path, metadata_file_path,
             AND the format specification from Stage 4b as shown below]
  - description: "Execute implementation for task {N}"

Format Injection: Include the format specification from Stage 4b in the prompt as a clearly-delimited section:

<artifact-format-specification>
## CRITICAL: Summary Format Requirements

You MUST follow this format specification exactly when writing the implementation summary.
Non-compliance will be caught by postflight validation.

{format_content from Stage 4b}
</artifact-format-specification>

Place this section AFTER the delegation context JSON and BEFORE any other instructions.

Memory Context Injection: If memory_context from Stage 4a is non-empty, include it in the prompt as a separate block:

{memory_context from Stage 4a -- already wrapped in <memory-context> tags}

Place the memory context block AFTER the format specification and BEFORE the task-specific instructions. Do NOT inject an empty <memory-context> block when no memories were retrieved.

DO NOT use Skill(general-implementation-agent) - this will FAIL.

The subagent will:

Load implementation context files
Parse plan and find resume point
Execute phases sequentially
Create/modify files as needed
Create implementation summary
Write metadata to specs/{NNN}_{SLUG}/.return-meta.json
Return a brief text summary (NOT JSON)

Stage 5a: Validate Subagent Return Format

If the subagent's text return parses as valid JSON, log a warning (v1 pattern instead of v2 file-based pattern). Non-blocking -- continue to read metadata file regardless.

Stage 5b: Self-Execution Fallback

CRITICAL: If you performed the work above WITHOUT using the Task tool (i.e., you read files, wrote artifacts, or updated metadata directly instead of spawning a subagent), you MUST write a .return-meta.json file now before proceeding to postflight. Use the schema from return-metadata-file.md with status value "implemented" and the appropriate artifact information.

If you DID use the Task tool (Stage 5), skip this stage -- the subagent already wrote the metadata.

Postflight (ALWAYS EXECUTE)

The following stages MUST execute after work is complete, whether the work was done by a subagent (Stage 5) or inline (Stage 5b). Do NOT skip these stages for any reason.

Stage 6: Parse Subagent Return (Read Metadata File)

Read the metadata file:

metadata_file="specs/${padded_num}_${project_name}/.return-meta.json"

if [ -f "$metadata_file" ] && jq empty "$metadata_file" 2>/dev/null; then
    status=$(jq -r '.status' "$metadata_file")
    artifact_path=$(jq -r '.artifacts[0].path // ""' "$metadata_file")
    artifact_type=$(jq -r '.artifacts[0].type // ""' "$metadata_file")
    artifact_summary=$(jq -r '.artifacts[0].summary // ""' "$metadata_file")
    phases_completed=$(jq -r '.metadata.phases_completed // 0' "$metadata_file")
    phases_total=$(jq -r '.metadata.phases_total // 0' "$metadata_file")

    # Extract completion_data fields (if present)
    completion_summary=$(jq -r '.completion_data.completion_summary // ""' "$metadata_file")
    claudemd_suggestions=$(jq -r '.completion_data.claudemd_suggestions // ""' "$metadata_file")
    roadmap_items=$(jq -c '.completion_data.roadmap_items // []' "$metadata_file")
    memory_candidates=$(jq -c '.memory_candidates // []' "$metadata_file")
else
    echo "Error: Invalid or missing metadata file"
    status="failed"
fi

Stage 6a: Validate Artifact Content

If subagent status indicates success ("implemented" or "partial") and artifact_path is non-empty, validate the summary artifact against format requirements. This is non-blocking -- warnings are logged but do not prevent postflight from completing.

if [ "$status" = "implemented" ] || [ "$status" = "partial" ]; then
    if [ -n "$artifact_path" ] && [ -f "$artifact_path" ]; then
        echo "Validating summary artifact..."
        if ! bash .claude/scripts/validate-artifact.sh "$artifact_path" summary --fix; then
            echo "WARNING: Summary artifact has format issues (non-blocking). Review output above."
        fi
    fi
fi

Note: The --fix flag attempts auto-repair of missing metadata fields. Validation failures are logged but do not block status update or git commit.

Stage 7: Update Task Status (Postflight)

If status is "implemented":

Step 1: Run the centralized status update script to update state.json (status -> "completed", timestamps), TODO.md ([IMPLEMENTING] -> [COMPLETED] in task entry + Task Order), and plan file (status -> [COMPLETED]):

bash .claude/scripts/update-task-status.sh postflight "$task_number" implement "$session_id"

Step 2: Add completion_summary to state.json (implementer-specific, not covered by centralized script):

if [ -n "$completion_summary" ]; then
    jq --arg summary "$completion_summary" \
      '(.active_projects[] | select(.project_number == '$task_number')).completion_summary = $summary' \
      specs/state.json > specs/tmp/state.json && mv specs/tmp/state.json specs/state.json
fi

Step 3: Add task-type-specific completion fields (implementer-specific):

# For meta tasks: add claudemd_suggestions
if [ "$task_type" = "meta" ] && [ -n "$claudemd_suggestions" ]; then
    jq --arg suggestions "$claudemd_suggestions" \
      '(.active_projects[] | select(.project_number == '$task_number')).claudemd_suggestions = $suggestions' \
      specs/state.json > specs/tmp/state.json && mv specs/tmp/state.json specs/state.json
fi

# For non-meta tasks: add roadmap_items (if present and non-empty)
if [ "$task_type" != "meta" ] && [ "$roadmap_items" != "[]" ] && [ -n "$roadmap_items" ]; then
    jq --argjson items "$roadmap_items" \
      '(.active_projects[] | select(.project_number == '$task_number')).roadmap_items = $items' \
      specs/state.json > specs/tmp/state.json && mv specs/tmp/state.json specs/state.json
fi

Step 4: Propagate memory candidates (if any) with append semantics:

if [ "$memory_candidates" != "[]" ] && [ -n "$memory_candidates" ]; then
    # Append new candidates to existing array (append semantics, not overwrite)
    jq --argjson new_candidates "$memory_candidates" \
      '(.active_projects[] | select(.project_number == '$task_number')).memory_candidates =
        ((.active_projects[] | select(.project_number == '$task_number')).memory_candidates // []) + $new_candidates' \
      specs/state.json > specs/tmp/state.json && mv specs/tmp/state.json specs/state.json
fi

Note: Uses // [] fallback and + append so research candidates (from skill-researcher) and implementation candidates coexist on the same task entry.

Step 5: Remove from Recommended Order section (non-blocking, not covered by centralized script):

if source "$PROJECT_ROOT/.claude/scripts/update-recommended-order.sh" 2>/dev/null; then
    remove_from_recommended_order "$task_number" || echo "Note: Failed to update Recommended Order"
fi

If status is "partial":

Keep status as "implementing" but update resume point. This path remains inline because the centralized update-task-status.sh maps postflight:implement to "completed" only -- it has no "partial" mapping.

jq --arg ts "$(date -u +%Y-%m-%dT%H:%M:%SZ)" \
   --argjson phase "$phases_completed" \
  '(.active_projects[] | select(.project_number == '$task_number')) |= . + {
    last_updated: $ts,
    resume_phase: ($phase + 1)
  }' specs/state.json > specs/tmp/state.json && mv specs/tmp/state.json specs/state.json

TODO.md stays as [IMPLEMENTING].

Update plan file (if exists): Update the Status field to [PARTIAL]:

.claude/scripts/update-plan-status.sh "$task_number" "$project_name" "PARTIAL"

On failed: Keep status as "implementing" for retry. Do not update plan file (leave as [IMPLEMENTING] for retry).

Stage 8: Link Artifacts

Add artifact to state.json with summary.

IMPORTANT: Use two-step jq pattern to avoid Issue #1132 escaping bug. See jq-escaping-workarounds.md.

if [ -n "$artifact_path" ]; then
    # Step 1: Filter out existing summary artifacts (use "| not" pattern to avoid != escaping - Issue #1132)
    jq '(.active_projects[] | select(.project_number == '$task_number')).artifacts =
        [(.active_projects[] | select(.project_number == '$task_number')).artifacts // [] | .[] | select(.type == "summary" | not)]' \
      specs/state.json > specs/tmp/state.json && mv specs/tmp/state.json specs/state.json

    # Step 2: Add new summary artifact
    jq --arg path "$artifact_path" \
       --arg type "$artifact_type" \
       --arg summary "$artifact_summary" \
      '(.active_projects[] | select(.project_number == '$task_number')).artifacts += [{"path": $path, "type": $type, "summary": $summary}]' \
      specs/state.json > specs/tmp/state.json && mv specs/tmp/state.json specs/state.json
fi

Update TODO.md (if implemented): Link artifact using the automated script:

bash .claude/scripts/link-artifact-todo.sh $task_number '**Summary**' '**Description**' "$artifact_path"

If the script exits non-zero, log a warning but continue (linking errors are non-blocking).

Stage 9: Git Commit

Commit changes with session ID:

git add -A
git commit -m "task ${task_number}: complete implementation

Session: ${session_id}

Stage 10: Cleanup

Remove marker and metadata files:

rm -f "specs/${padded_num}_${project_name}/.postflight-pending"
rm -f "specs/${padded_num}_${project_name}/.postflight-loop-guard"
rm -f "specs/${padded_num}_${project_name}/.return-meta.json"

Stage 11: Return Brief Summary

Return a brief text summary (NOT JSON). Example:

Implementation completed for task {N}:
- All {phases_total} phases executed successfully
- Key changes: {summary of changes}
- Created summary at specs/{NNN}_{SLUG}/summaries/MM_{short-slug}-summary.md
- Status updated to [COMPLETED]
- Changes committed

Error Handling

See rules/error-handling.md for general patterns. Skill-specific behaviors:

Input validation errors: Return immediately with error message
Metadata file missing: Keep status as "implementing", do not cleanup marker, report to user
Git commit failure: Non-blocking (log and continue)
Subagent timeout: Return partial status, keep "implementing" for resume

Pre-Delegation Boundary

Before spawning the implementation sub-agent, this skill MUST NOT:

Read source files - Source files are read by the sub-agent, not the lead
Grep or glob the codebase - Codebase exploration is sub-agent work
Use MCP tools - Domain tools (LSP, build, etc.) are for sub-agent use only
Analyze source code - Code analysis belongs to the implementation agent
Run build or test commands - Verification is done by the sub-agent

The pre-delegation phase is LIMITED TO:

Reading the plan file to locate phases and extract the plan path
Reading state.json and TODO.md for status updates
Preparing the delegation context JSON
Reading the summary format file for injection (Stage 4b)
Spawning the sub-agent with the Task tool

MUST NOT (Postflight Boundary)

After the agent returns -- whether with status implemented, partial, or failed -- this skill MUST proceed immediately to Stage 6 (read metadata file). The skill MUST NOT:

Read source files - Source files were the subagent's responsibility
Edit source files - All implementation work is done by the subagent
Run build/test commands - Verification is done by the subagent
Use MCP tools - Domain tools are for subagent use only
Grep or glob the codebase - Analysis is subagent work
Write summary/reports - Artifact creation is done by the subagent

PROHIBITION: If the subagent returned partial or failed status, the lead skill MUST NOT attempt to continue, complete, or "fill in" the subagent's work. Report the partial/failed status and let the user re-run /implement to resume.

The postflight phase is LIMITED TO:

Reading agent metadata file (.return-meta.json)
Updating state.json via jq
Updating TODO.md status marker via Edit or script
Linking artifacts in state.json
Git commit
Cleanup of temp/marker files

Reference: @.claude/context/standards/postflight-tool-restrictions.md

skill-implementer