feat(extensions): add pipeline extension for end-to-end SDD workflow

Moves the pipeline command from templates/commands/ to extensions/
as requested in PR #1967 review. Provides automatic progression
through specify → clarify → plan → tasks → analyze → implement.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: RchrdHndrcks

extensions/pipeline/commands/pipeline.md

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+---
+description: "Run the full speckit workflow end-to-end (specify → clarify → plan → tasks → analyze → implement) with automatic progression between steps."
+---
+
+## User Input
+
+```text
+$ARGUMENTS
+```
+
+You **MUST** consider the user input before proceeding (if not empty).
+
+## Pipeline Overview
+
+This command orchestrates the full Spec-Driven Development workflow automatically. You MUST execute each step in sequence by invoking the corresponding `/speckit.*` command. After each step completes, proceed immediately to the next one WITHOUT returning control to the user, UNLESS a step explicitly requires user input (e.g., clarification questions).
+
+**Pipeline Steps:**
+
+1. `/speckit.specify` — Create feature specification
+2. `/speckit.clarify` — Resolve ambiguities (interactive: user answers questions)
+3. `/speckit.plan` — Generate technical plan
+4. `/speckit.tasks` — Break plan into actionable tasks
+5. `/speckit.analyze` — Cross-artifact consistency analysis
+6. `/speckit.implement` — Execute all tasks
+
+## Execution Rules
+
+### Auto-Progression (CRITICAL)
+
+- After each step completes successfully, **immediately invoke the next step**. Do NOT ask the user "shall I proceed?" or "ready for the next step?". Just do it.
+- The ONLY reasons to pause are:
+  - A step requires user input (e.g., `/speckit.clarify` asking clarification questions, or `/speckit.implement` asking about incomplete checklists)
+  - `/speckit.analyze` reports CRITICAL issues (ask user whether to proceed or fix first)
+  - A step fails with an error
+- When user input is received and the step completes, resume auto-progression to the next step.
+
+### Step Invocation
+
+- Use the agent's native mechanism to invoke each slash command (e.g., Claude Code's Skill tool, Copilot's chat commands).
+- Step 1 (`/speckit.specify`): Pass the full `$ARGUMENTS` as the feature description.
+- Steps 2-6: Invoke with no arguments (they auto-detect the feature context from the current branch and feature directory).
+
+### Error Handling
+
+- If any step fails, report the error and suggest the corrective action. Do NOT auto-proceed past a failed step.
+- If `/speckit.analyze` reports CRITICAL issues, pause and present the user with two options:
+  1. Fix the issues before proceeding to implementation
+  2. Proceed to implementation despite the issues
+
+### Progress Reporting
+
+- Before each step, output a single line: `## Pipeline Step N/6: [step name]`
+- After each step completes, output: `Step N/6 complete. Proceeding to next step...`
+- Keep progress reporting minimal — the individual commands already produce their own output.
+
+## Start
+
+Begin by invoking `/speckit.specify` with the feature description from `$ARGUMENTS`. If `$ARGUMENTS` is empty, ask the user for a feature description before starting.

extensions/pipeline/extension.yml

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+schema_version: "1.0"
+
+extension:
+  id: pipeline
+  name: Spec Kit Pipeline
+  version: 1.0.0
+  description: End-to-end SDD workflow orchestration — runs specify, clarify, plan, tasks, analyze, and implement in sequence with automatic progression.
+  author: RchrdHndrcks
+  repository: https://github.com/RchrdHndrcks/spec-kit
+  license: MIT
+
+requires:
+  speckit_version: ">=0.1.0"
+  commands:
+    - "speckit.specify"
+    - "speckit.clarify"
+    - "speckit.plan"
+    - "speckit.tasks"
+    - "speckit.analyze"
+    - "speckit.implement"
+
+provides:
+  commands:
+    - name: speckit.pipeline.run
+      file: commands/pipeline.md
+      description: Run the full speckit workflow end-to-end (specify → clarify → plan → tasks → analyze → implement) with automatic progression between steps.
+      aliases:
+        - speckit.pipeline
+
+tags:
+  - workflow
+  - automation
+  - pipeline