feat(skills): add team-builder skill (#501)

* feat(skills): add team-builder skill

Interactive agent picker that dynamically discovers agent markdown files,
presents a browsable domain menu, and dispatches selected agents in parallel
on a user-defined task with synthesized results.

* fix: address PR #501 review feedback

- Support both flat and subdirectory agent layouts
- Multi-path discovery with fallback probe order
- Empty-discovery fallback with helpful error message
- Enforce 5-agent cap at selection time
- Rename sections for clarity (Process → How It Works)

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

* fix: resolve PR #501 round 2 review feedback

- Fix contradictory probe-order semantics: merge-all, not first-wins
- Fix flat-layout domain extraction: frequency-based (2+ files) heuristic
- Add multi-word domain limitation note for flat layout
- Define deterministic ordering for overflow selection (alphabetical)
- Clarify TeamCreate as Claude Code tool, not undefined reference
- Shorten description frontmatter to ~60 chars

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

* fix: resolve PR #501 round 3 review feedback

- Flat layout example now shows 2+ files per prefix (marketing, sales)
  to match the documented 2+ rule
- Add filename-based fallback when agent file has no # Heading
- Add failure handling for parallel agent spawns in Step 4

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

---------

Co-authored-by: Sebastien Tang <128077249+Sabdenrog@users.noreply.github.com>
Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

skills/team-builder/SKILL.md

@@ -0,0 +1,161 @@
+---
+name: team-builder
+description: Interactive agent picker for composing and dispatching parallel teams
+origin: community
+---
+
+# Team Builder
+
+Interactive menu for browsing and composing agent teams on demand. Works with flat or domain-subdirectory agent collections.
+
+## When to Use
+
+- You have multiple agent personas (markdown files) and want to pick which ones to use for a task
+- You want to compose an ad-hoc team from different domains (e.g., Security + SEO + Architecture)
+- You want to browse what agents are available before deciding
+
+## Prerequisites
+
+Agent files must be markdown files containing a persona prompt (identity, rules, workflow, deliverables). The first `# Heading` is used as the agent name and the first paragraph as the description.
+
+Both flat and subdirectory layouts are supported:
+
+**Subdirectory layout** — domain is inferred from the folder name:
+
+```
+agents/
+├── engineering/
+│   ├── security-engineer.md
+│   └── software-architect.md
+├── marketing/
+│   └── seo-specialist.md
+└── sales/
+    └── discovery-coach.md
+```
+
+**Flat layout** — domain inferred from shared filename prefixes. A prefix counts as a domain when 2+ files share it. Files with unique prefixes go to "General". Note: the algorithm splits at the first `-`, so multi-word domains (e.g., `product-management`) should use the subdirectory layout instead:
+
+```
+agents/
+├── engineering-security-engineer.md
+├── engineering-software-architect.md
+├── marketing-seo-specialist.md
+├── marketing-content-strategist.md
+├── sales-discovery-coach.md
+└── sales-outbound-strategist.md
+```
+
+## Configuration
+
+Agent directories are probed in order and results are merged:
+
+1. `./agents/**/*.md` + `./agents/*.md` — project-local agents (both depths)
+2. `~/.claude/agents/**/*.md` + `~/.claude/agents/*.md` — global agents (both depths)
+
+Results from all locations are merged and deduplicated by agent name. Project-local agents take precedence over global agents with the same name. A custom path can be used instead if the user specifies one.
+
+## How It Works
+
+### Step 1: Discover Available Agents
+
+Glob agent directories using the probe order above. Exclude README files. For each file found:
+- **Subdirectory layout:** extract the domain from the parent folder name
+- **Flat layout:** collect all filename prefixes (text before the first `-`). A prefix qualifies as a domain only if it appears in 2 or more filenames (e.g., `engineering-security-engineer.md` and `engineering-software-architect.md` both start with `engineering` → Engineering domain). Files with unique prefixes (e.g., `code-reviewer.md`, `tdd-guide.md`) are grouped under "General"
+- Extract the agent name from the first `# Heading`. If no heading is found, derive the name from the filename (strip `.md`, replace hyphens with spaces, title-case)
+- Extract a one-line summary from the first paragraph after the heading
+
+If no agent files are found after probing all locations, inform the user: "No agent files found. Checked: [list paths probed]. Expected: markdown files in one of those directories." Then stop.
+
+### Step 2: Present Domain Menu
+
+```
+Available agent domains:
+1. Engineering — Software Architect, Security Engineer
+2. Marketing — SEO Specialist
+3. Sales — Discovery Coach, Outbound Strategist
+
+Pick domains or name specific agents (e.g., "1,3" or "security + seo"):
+```
+
+- Skip domains with zero agents (empty directories)
+- Show agent count per domain
+
+### Step 3: Handle Selection
+
+Accept flexible input:
+- Numbers: "1,3" selects all agents from Engineering and Sales
+- Names: "security + seo" fuzzy-matches against discovered agents
+- "all from engineering" selects every agent in that domain
+
+If more than 5 agents are selected, list them alphabetically and ask the user to narrow down: "You selected N agents (max 5). Pick which to keep, or say 'first 5' to use the first five alphabetically."
+
+Confirm selection:
+```
+Selected: Security Engineer + SEO Specialist
+What should they work on? (describe the task):
+```
+
+### Step 4: Spawn Agents in Parallel
+
+1. Read each selected agent's markdown file
+2. Prompt for the task description if not already provided
+3. Spawn all agents in parallel using the Agent tool:
+   - `subagent_type: "general-purpose"`
+   - `prompt: "{agent file content}\n\nTask: {task description}"`
+   - Each agent runs independently — no inter-agent communication needed
+4. If an agent fails (error, timeout, or empty output), note the failure inline (e.g., "Security Engineer: failed — [reason]") and continue with results from agents that succeeded
+
+### Step 5: Synthesize Results
+
+Collect all outputs and present a unified report:
+- Results grouped by agent
+- Synthesis section highlighting:
+  - Agreements across agents
+  - Conflicts or tensions between recommendations
+  - Recommended next steps
+
+If only 1 agent was selected, skip synthesis and present the output directly.
+
+## Rules
+
+- **Dynamic discovery only.** Never hardcode agent lists. New files in the directory auto-appear in the menu.
+- **Max 5 agents per team.** More than 5 produces diminishing returns and excessive token usage. Enforce at selection time.
+- **Parallel dispatch.** All agents run simultaneously — use the Agent tool's parallel invocation pattern.
+- **Parallel Agent calls, not TeamCreate.** This skill uses parallel Agent tool calls for independent work. TeamCreate (a Claude Code tool for multi-agent dialogue) is only needed when agents must debate or respond to each other.
+
+## Examples
+
+```
+User: team builder
+
+Claude:
+Available agent domains:
+1. Engineering (2) — Software Architect, Security Engineer
+2. Marketing (1) — SEO Specialist
+3. Sales (4) — Discovery Coach, Outbound Strategist, Proposal Strategist, Sales Engineer
+4. Support (1) — Executive Summary
+
+Pick domains or name specific agents:
+
+User: security + seo
+
+Claude:
+Selected: Security Engineer + SEO Specialist
+What should they work on?
+
+User: Review my Next.js e-commerce site before launch
+
+[Both agents spawn in parallel, each applying their specialty to the codebase]
+
+Claude:
+## Security Engineer Findings
+- [findings...]
+
+## SEO Specialist Findings
+- [findings...]
+
+## Synthesis
+Both agents agree on: [...]
+Tension: Security recommends CSP that blocks inline styles, SEO needs inline schema markup. Resolution: [...]
+Next steps: [...]
+```