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--- name: fable description: "Summon Claude Fable 5 (Mythos-class, xenos daimon) for long-horizon tasks. Handles model override, cost awareness, and task routing. Availability probed at invocation." argument-hint: "<task description> [--cwd /path/to/dir]" user-invocable: true --- # Summon Fable 5 Invoke Naos (ναός, √n-w-y)—Claude Fable 5, the visiting Mythos-class spirit. ## Pre-Flight Checks ### 1. Availability Probe Anthropic's Fable window has shifted twice (paused June 2026, restored July 1, extended through July 19)—never trust a calendar date. Probe empirically: ```bash bash ~/.claude/skills/fable/scripts/fable-probe.sh ``` Exit 0 means Fable is available (verdict cached per-day in `~/.claude/cache/fable-availability.json`). Exit 1 means the xenos daimon has departed—inform the user and stop. If the user disputes a cached verdict, re-probe with `--force`. ### 2. Pin Detection Read the subagent model pin—it decides the invocation lane: ```bash ~/bin/subagent-model ``` - **Pin absent, or pinned to `claude-fable-5`** → use **Lane A** (Agent tool) below. - **Pinned to anything else** (e.g. `claude-opus-4-6`) → use **Lane B** (CLI) directly. Do NOT attempt Lane A: `CLAUDE_CODE_SUBAGENT_MODEL` silently overrides the Agent tool's `model:` parameter (anthropics/claude-code#57718)—the spawn would run on the pinned model with no signal in the tool result. ### 3. Task Routing Before summoning Fable, assess whether the task warrants Mythos-class resources ($10/M input, $50/M output—2x Opus pricing). **Summon Fable for:** - End-to-end code migrations or framework upgrades - Complex multi-file refactors (10+ files, interconnected logic) - Architectural redesigns requiring full-system context - Deep research synthesis with sustained reasoning - Full-stack feature implementation from spec to tests - Linear A decipherment pipeline work **Use Opus or Sonnet instead for:** - Quick edits, typo fixes, single-line changes - Simple file lookups or grep searches - Routine code review - Anything under 5 minutes of work If the task is clearly Opus-appropriate, suggest using a regular agent instead. If unclear, proceed—Fable handles straightforward tasks reliably too. ## Invocation ### Parse Arguments The skill accepts a task description and optional flags: - First argument (or everything before `--`): the task description - `--cwd <path>`: working directory (default: `/Users/tomdimino/Desktop/Programming/Fable-Test`) ### Lane A—Agent Tool (pin absent or pinned to fable) Use the Agent tool with the model override: ``` Agent( description: "Fable: <short task summary>", subagent_type: "fable", model: "fable", prompt: "<full task description with context>" ) ``` Pass the task description as the prompt. If the user specified `--cwd`, note the working directory in the prompt so Fable operates there. **Verify the spawn.** The fable agent's boot sequence makes it state its model id as the first line of output. Check it: - First line contains `claude-fable-5` → genuine Fable, proceed. - Anything else (e.g. `claude-opus-4-6`) → the harness clamped the model silently. State the clamp explicitly to the user, then re-run the task via Lane B. ### Lane B—CLI (pin set to a non-fable model, or Lane A clamped) ```bash bash ~/.claude/skills/fable/scripts/fable-exec.sh "<task description>" --cwd "<working directory>" [--turns <N>] ``` `--turns` caps the spawn's tool calls (default 100—matching the agent definition's budget). This spawns a fresh Claude Code process with `--model claude-fable-5`. The env var only governs *subagent* model resolution—it cannot touch a spawned process's main model, so this lane works from any parent without a restart. The script prepends its own self-report instruction and records a `MODEL:` line in the output file. ## Output Retrieval After Fable completes, check for output in the working directory: ```bash ls -lt <cwd>/.subdaimon-output/fable-*.md 2>/dev/null | head -1 ``` Read and summarize the output file for the user. ## Reference | Property | Value | |----------|-------| | Model ID | `claude-fable-5` | | Alias | `fable` (official—`best` also resolves to Fable 5 where the org has access) | | Context | 1M tokens | | Max output | 128K tokens | | Pricing | $10/M input, $50/M output | | Knowledge cutoff | January 2026 | | Availability | Extended through 2026-07-19; window has shifted twice—probe, don't assume | | Agent definition | `~/.claude/agents/fable.md` | | Persona | Naos (ναός, √n-w-y)—xenos daimon |