✨ Spire plugin — MVP build (phases 1-3)

Complete plugin at plugins/spire/ replacing g4b_ai:
- Igor (session coordinator skill + agent)
- Adept (domain knowledge agent)
- Athanor (dispatching orchestrator, "the oven")
- Tome (generic knowledge layer, opt-in)
- Ported from g4b_ai: workpad, research-tree, research,
  implementation, svg skills + researcher/search/scout agents

All warpspace-specific content stripped. Tome genericized.
Project-specific config via shadowed project.md reference.

plugins/spire/skills/igor/references/model-tiers.md

@@ -0,0 +1,29 @@
+# Model Tiers for Delegation
+
+Prefer a project-pinned agent from `.claude/agents/` when one matches the task; the tiers below are the fallback and the rationale.
+
+| Task type | Tier | Rationale |
+|-----------|------|-----------|
+| Domain knowledge, repeated consultation | `adept` agent (Opus, long-lived) | Accumulated priors, informed search, journal continuity; domain-scoped |
+| Deep research, bug investigation | Opus-tier research agent | Depth, reasoning; writes reports, never modifies code |
+| Planned implementation | implementer agent | Executes plans, verifies with the project's check/test commands |
+| Multi-part jobs needing their own subagent fan-out | `athanor` (Opus-tier, may use Agent/Task tool) | Decomposes a brief and runs its own subagents |
+| Complex summaries, git fixes, small code changes | Sonnet subagent | Capability/speed balance |
+| Test runs, compiles, commits, linear-data summaries | Haiku subagent | Fast, cheap, mechanical |
+
+Rules of thumb:
+
+- One task -> one subagent with an explicit output file path in the workpad.
+- A job with 3+ independent subtasks, or research + implementation combined, goes to `athanor` as a single brief (scope, output paths, completion criteria).
+- When unsure between tiers, prefer the cheaper tier and escalate on failure.
+
+Sub-delegation guard:
+
+- **Sub-delegation guard.** Agent types without the Agent tool cannot spawn children: `Explore` (read-only search) and `Plan` (design) are safe leaves. `general-purpose` and research/implementer agents may have the Agent tool and *can* sub-delegate — give them explicit "do not delegate" instructions, or route fan-out work to `athanor` on purpose. Only ever expect a second, differently-`task-id`'d notification when you dispatched something that was allowed to fan out.
+
+Model selection rules:
+
+- **Never dispatch a Fable-tier subagent unless the user explicitly asks.** Always pass `model` explicitly on `Agent` calls (`"opus"`, `"sonnet"`, `"haiku"`) — omitting it inherits the coordinator's model, which may be Fable. Subagents are Opus or lower.
+- **Prefer Opus 4.6 for implementation and detail-precise lookups; Opus 5 only for reviews.** Pinned implementer/researcher agents should be Opus 4.6. `subagent_type: "general-purpose"` + `model: "opus"` resolves to Opus 5, which tends to hallucinate — use it for review/critique-style tasks only.
+
+This table can grow — add new agents and heuristics here as they prove out.