feat(agents): add Hephaestus - autonomous deep worker agent (#1287)

* refactor(keyword-detector): split constants into domain-specific modules

* feat(shared): add requiresAnyModel and isAnyFallbackModelAvailable

* feat(config): add hephaestus to agent schemas

* feat(agents): add Hephaestus autonomous deep worker

* feat(cli): update model-fallback for hephaestus support

* feat(plugin): add hephaestus to config handler with ordering

* test(delegate-task): update tests for hephaestus agent

* docs: update AGENTS.md files for hephaestus

* docs: add hephaestus to READMEs

* chore: regenerate config schema

* fix(delegate-task): bypass requiresModel check when user provides explicit config

* docs(hephaestus): add 4-part context structure for explore/librarian prompts

* docs: fix review comments from cubic (non-breaking changes)

- Move Hephaestus from Primary Agents to Subagents (uses own fallback chain)
- Fix Hephaestus fallback chain documentation (claude-opus-4-5 → gemini-3-pro)
- Add settings.local.json to claude-code-hooks config sources
- Fix delegate_task parameters in ultrawork prompt (agent→subagent_type, background→run_in_background, add load_skills)
- Update line counts in AGENTS.md (index.ts: 788, manager.ts: 1440)

* docs: fix additional documentation inconsistencies from oracle review

- Fix delegate_task parameters in Background Agents example (docs/features.md)
- Fix Hephaestus fallback chain in root AGENTS.md to match model-requirements.ts

* docs: clarify Hephaestus has no fallback (requires gpt-5.2-codex only)

Hephaestus uses requiresModel constraint - it only activates when gpt-5.2-codex
is available. The fallback chain in code is unreachable, so documentation
should not mention fallbacks.

* fix(hephaestus): remove unreachable fallback chain entries

Hephaestus has requiresModel: gpt-5.2-codex which means the agent only
activates when that specific model is available. The fallback entries
(claude-opus-4-5, gemini-3-pro) were unreachable and misleading.

---------

Co-authored-by: justsisyphus <justsisyphus@users.noreply.github.com>

src/shared/agent-variant.test.ts

@@ -95,22 +95,22 @@ describe("resolveVariantForModel", () => {
     expect(variant).toBe("max")
   })
 
-  test("returns correct variant for openai provider", () => {
-    // given
+  test("returns correct variant for openai provider (hephaestus agent)", () => {
+    // #given hephaestus has openai/gpt-5.2-codex with variant "medium" in its chain
     const config = {} as OhMyOpenCodeConfig
-    const model = { providerID: "openai", modelID: "gpt-5.2" }
+    const model = { providerID: "openai", modelID: "gpt-5.2-codex" }
 
-    // when
-    const variant = resolveVariantForModel(config, "sisyphus", model)
+    // #when
+    const variant = resolveVariantForModel(config, "hephaestus", model)
 
     // then
     expect(variant).toBe("medium")
   })
 
-  test("returns undefined for provider with no variant in chain", () => {
-    // given
+  test("returns undefined for provider not in sisyphus chain", () => {
+    // #given openai is not in sisyphus fallback chain anymore
     const config = {} as OhMyOpenCodeConfig
-    const model = { providerID: "google", modelID: "gemini-3-pro" }
+    const model = { providerID: "openai", modelID: "gpt-5.2" }
 
     // when
     const variant = resolveVariantForModel(config, "sisyphus", model)