Feature Request: Implement parallel execution for (P) marked tasks in spec-impl

[yahsan2]

Summary

The tasks-parallel-analysis.md rule file defines (P) markers for identifying parallel-capable tasks, but spec-impl command does not utilize these markers for actual parallel execution.

This issue applies to Claude Code Subagents mode:

npx cc-sdd@latest --claude-agent   # Claude Code Subagents

Current Behavior

• tasks-parallel-analysis.md provides rules for marking tasks with (P) (e.g., - [ ] 2.1 (P) Build background worker)
• spec-tasks generates tasks with (P) markers when parallel criteria are met
• spec-impl executes all tasks sequentially, ignoring (P) markers

Expected Behavior

When executing multiple tasks without --sequential flag:

• Tasks marked with (P) should be executed in parallel (multiple subagent invocations in a single message)
• Tasks without (P) should continue to execute sequentially to respect dependencies

Proposed Implementation

1. Add --sequential flag to spec-impl command
2. Detect (P) markers in selected tasks from tasks.md
3. When --sequential is NOT provided:
   • Group (P) marked tasks and invoke multiple spec-tdd-impl-agent subagents in parallel
   • Execute non-(P) tasks sequentially
4. When --sequential is provided:
   • Execute all tasks sequentially (ignore (P) markers)

Example Usage

# Parallel execution for (P) marked tasks (default)
/kiro:spec-impl my-feature 1,2,3

# Force sequential execution
/kiro:spec-impl my-feature 1,2,3 --sequential

Related Files

• docs/settings/rules/tasks-parallel-analysis.md - Defines (P) marking conventions
• .claude/commands/kiro/spec-impl.md - Command implementation (needs update)