feat(#1014): add Claude Fable 5 model config (#1015)

(cherry picked from commit 76f42ddb4b)

docs/CONFIGURATION.md

@@ -144,7 +144,7 @@ GSD stores project settings in `.planning/config.json`. Created during `/gsd-new
 | `model_profile` | enum | `quality`, `balanced`, `budget`, `adaptive`, `inherit` | `balanced` | Model tier for each agent (see [Model Profiles](#model-profiles)). `adaptive` was added per [#1713](https://github.com/open-gsd/gsd-core/issues/1713) / [#1806](https://github.com/open-gsd/gsd-core/issues/1806) and resolves the same way as the other tiers under runtime-aware profiles. |
 | `runtime` | string | `claude`, `codex`, or any string | (none) | Active runtime for [runtime-aware profile resolution](#runtime-aware-profiles-2517). When set, profile tiers (opus/sonnet/haiku) resolve to runtime-native model IDs. Today only the Codex install path emits per-agent model IDs from this resolver; other runtimes (`opencode`, `gemini`, `qwen`, `copilot`, …) consume the resolver at spawn time and gain dedicated install-path support in [#2612](https://github.com/open-gsd/gsd-core/issues/2612). When unset (default), behavior is unchanged from prior versions. Added in v1.39 |
 | `model_profile_overrides.<runtime>.<tier>` | string \| object | per-runtime tier override | (none) | Override the runtime-aware tier mapping for a specific `(runtime, tier)`. Tier is one of `opus`, `sonnet`, `haiku`. Value is either a model ID string (e.g. `"gpt-5-pro"`) or `{ model, reasoning_effort }`. See [Runtime-Aware Profiles](#runtime-aware-profiles-2517). Added in v1.39 |
-| `model_policy.provider` | string | `openai`, `anthropic`, `google`, `qwen`, `generic` | (none) | Declares the model provider. Known providers (`openai`, `anthropic`, `google`, `qwen`) unlock catalog-backed presets. `generic` treats all model IDs as opaque strings — no prefix inference, no reasoning-effort defaults. `model_policy.runtime_tiers` resolves before legacy `model_profile_overrides`. See [Model Policy Presets](#model-policy-presets-model_policy--added-in-v142). Added in v1.42 ([#49](https://github.com/open-gsd/gsd-core/issues/49)) |
+| `model_policy.provider` | string | `openai`, `anthropic`, `anthropic-fable`, `google`, `qwen`, `generic` | (none) | Declares the model provider. Known providers (`openai`, `anthropic`, `anthropic-fable`, `google`, `qwen`) unlock catalog-backed presets. `generic` treats all model IDs as opaque strings — no prefix inference, no reasoning-effort defaults. `model_policy.runtime_tiers` resolves before legacy `model_profile_overrides`. See [Model Policy Presets](#model-policy-presets-model_policy--added-in-v142). Added in v1.42 ([#49](https://github.com/open-gsd/gsd-core/issues/49)) |
 | `model_policy.budget` | enum | `high`, `medium`, `low` | (none) | Selects a budget tier when using a known provider. GSD materializes the matching catalog preset into explicit tier mappings at resolve time. Ignored when `provider` is `generic` or `custom`. Added in v1.42 ([#49](https://github.com/open-gsd/gsd-core/issues/49)) |
 | `model_policy.high` | string | model ID | (none) | High-cost tier model ID for `generic`/`custom` provider. Used when `provider: "generic"` or `"custom"`. Added in v1.42 ([#49](https://github.com/open-gsd/gsd-core/issues/49)) |
 | `model_policy.medium` | string | model ID | (none) | Medium-cost tier model ID for `generic`/`custom` provider. Added in v1.42 ([#49](https://github.com/open-gsd/gsd-core/issues/49)) |
@@ -159,7 +159,7 @@ GSD stores project settings in `.planning/config.json`. Created during `/gsd-new
 | `project_code` | string | any short string | (none) | Prefix for phase directory names (e.g., `"ABC"` produces `ABC-01-setup/`). Added in v1.31 |
 | `phase_id_convention` | enum | `"milestone-prefixed"`, `null` | `null` | Phase ID naming convention. `null` = legacy numeric IDs (`Phase 1`, `Phase 2`). `"milestone-prefixed"` = globally unique IDs that encode the enclosing milestone (`Phase 1-01`, `Phase 1-02`). Run `gsd-tools roadmap upgrade --convention milestone-prefixed` to migrate an existing ROADMAP.md. |
 | `response_language` | string | language code | (none) | Language for agent responses (e.g., `"pt"`, `"ko"`, `"ja"`). Propagates to all spawned agents for cross-phase language consistency. Added in v1.32 |
-| `context_window` | number | any integer | `200000` | Context window size in tokens. Set `1000000` for 1M-context models (e.g., `claude-opus-4-7[1m]`). Values `>= 500000` enable adaptive context enrichment (full-body reads of prior SUMMARY.md, deeper anti-pattern reads). Configured via `/gsd-config --advanced`. |
+| `context_window` | number | any integer | `200000` | Context window size in tokens. Set `1000000` for 1M-context models (e.g., `claude-fable-5`). Values `>= 500000` enable adaptive context enrichment (full-body reads of prior SUMMARY.md, deeper anti-pattern reads). Configured via `/gsd-config --advanced`. |
 | `context_profile` | string | `dev`, `research`, `review` | (none) | Execution context preset that applies a pre-configured bundle of mode, model, and workflow settings for the current type of work. Added in v1.34 |
 | `claude_md_path` | string | any file path | `./CLAUDE.md` | Custom output path for the generated CLAUDE.md file. Useful for monorepos or projects that need CLAUDE.md in a non-root location. Defaults to `./CLAUDE.md` at the project root. Added in v1.36 |
 | `claude_md_assembly.mode` | enum | `embed`, `link` | `embed` | Controls how managed sections are written into CLAUDE.md. `embed` (default) inlines content between GSD markers. `link` writes `@.planning/<source-path>` instead — Claude Code expands the reference at runtime, reducing CLAUDE.md size by ~65% on typical projects. `link` only applies to sections that have a real source file; `workflow` and fallback sections always embed. Per-block overrides: `claude_md_assembly.blocks.<section>` (e.g. `claude_md_assembly.blocks.architecture: link`). Added in v1.38 |
@@ -1284,7 +1284,7 @@ Choose a provider and budget level via the settings workflow; GSD writes the can
 }
 ```
 
-Known providers: `openai`, `anthropic`, `google`, `qwen`. Budget levels: `high`, `medium`, `low`.
+Known providers: `openai`, `anthropic`, `anthropic-fable`, `google`, `qwen`. Budget levels: `high`, `medium`, `low`. Use `anthropic` to keep the Opus 4.8-backed Claude preset, or `anthropic-fable` to opt into Claude Fable 5 for high-budget top-tier routing.
 
 For advanced per-runtime control, `runtime_tiers` accepts explicit entries using the internal profile tier names (`opus`, `sonnet`, `haiku`):