feat(skills): add model-family hint files for agent:bootstrap injection (anthropic/openai/generic)

skills/llm-tool-best-practices/hints/anthropic.md

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+# MODEL_HINTS.md — Anthropic/Claude Tool Best Practices
+
+Active model family: **Anthropic (Claude)**
+
+When writing or evaluating skills/tools for this session, apply these rules:
+
+## Schema
+- Use `input_schema` (not `parameters`) for tool definitions.
+- Add `strict: true` for production tools — guarantees schema conformance via structured outputs.
+- Use `input_examples` array for tools with complex inputs, nested objects, or format-sensitive params.
+
+## Descriptions
+- Write **3–4+ sentences** per tool: what it does, when to use/not use it, what each param means, what it returns, caveats.
+- This is the highest-leverage factor in Claude's tool selection accuracy.
+
+## Model selection
+- Use **Claude Opus** for complex/multi-tool tasks or ambiguous queries.
+- Use **Claude Haiku** for simple well-defined tools only — it may infer missing params.
+
+## Tool design
+- Consolidate related operations into fewer tools (e.g. one `github_pr` tool with action param vs three separate tools).
+- Use `service_resource_verb` namespacing: `github_issues_search`, `slack_channel_send`.
+- Return only high-signal fields. Prefer semantic names/slugs over raw UUIDs.
+- Bound response size. Truncation messages should be actionable (tell Claude what to do next).
+- For errors: plain-language messages, not stack traces.
+
+## Safety
+- Least privilege on all tool permissions.
+- Guard destructive/irreversible actions with confirmation or human-in-the-loop.
+- Validate all tool inputs before acting.