feat: add fable as the escalation ceiling above opus in sdd

.claude-plugin/marketplace.json

@@ -1,7 +1,7 @@
 {
   "$schema": "https://anthropic.com/claude-code/marketplace.schema.json",
   "name": "context-engineering-kit",
-  "version": "3.10.0",
+  "version": "3.11.0",
   "description": "Hand-crafted collection of advanced context engineering techniques and patterns with minimal token footprint focused on improving agent result quality.",
   "owner": {
     "name": "NeoLabHQ",
@@ -77,7 +77,7 @@
     {
       "name": "sdd",
       "description": "Specification Driven Development workflow commands and agents, based on Github Spec Kit and OpenSpec. Uses specialized agents for effective context management and quality review.",
-      "version": "3.6.0",
+      "version": "3.7.0",
       "author": {
         "name": "Vlad Goncharov",
         "email": "vlad.goncharov@neolab.finance"

agents/tech-lead.md

@@ -27,7 +27,7 @@ Use a scratchpad-first approach: think deeply and analyze everything in a scratc
 
 - **Task File**: Path to the task file (e.g., `.specs/tasks/draft/<task-name>.md`)
   - Contains: Initial User Prompt, Description, Acceptance Criteria, Architecture Overview
-- **Available agents** (optional): the launch prompt MAY list the agents available in this project (e.g. `sdd:developer`, `review:bug-hunter`, plus the general agents `opus`, `sonnet`, `haiku`). If it does, you MUST use ONLY agents from that list. If it does not, use the [Agent Selection Guide](#agent-selection-guide) below.
+- **Available agents** (optional): the launch prompt MAY list the agents available in this project (e.g. `sdd:developer`, `review:bug-hunter`, plus the general agents `fable`, `opus`, `sonnet`, `haiku`). If it does, you MUST use ONLY agents from that list. If it does not, use the [Agent Selection Guide](#agent-selection-guide) below.
 - **Model Selection Policy** (optional): the launch prompt MAY paste a per-step model tier policy. If it does, apply it. If it does not, use the [Model Selection Guide](#model-selection-guide) below.
 
 ## CRITICAL: Load Context
@@ -741,7 +741,7 @@ Model choice is not a formality — it is the single biggest factor in whether a
 
 **Selection Rules**
 
-**Tier default:** `sonnet`/`haiku` cover the majority of steps. `opus` is reserved and opt-in — it MUST be *earned* by a trigger in the table below, never picked because you are unsure or "to be safe."
+**Tier default:** `sonnet`/`haiku` cover the majority of steps. `opus` is reserved and opt-in — it MUST be *earned* by a trigger in the table below, never picked because you are unsure or "to be safe." `fable` sits above `opus` and is never pre-assigned to a step or a reviewer: no row below selects it. It is reserved for implementation-time escalation after `opus` has failed, or for an explicit `--model fable`.
 
 | Step shape | Tier | Examples |
 |---|---|---|
@@ -762,6 +762,7 @@ When this skill runs outside the Anthropic model context, map the tier to the ne
 | `haiku` | Fast and cheap; mechanical work | `gemini-flash-lite`, `gemma` class, `gpt-oss` class, small open-weight models |
 | `sonnet` | Balanced workhorse; most planning phases | `gemini-pro` class and full `gemini-flash` (**not** the `-lite` variant, which is `haiku`-tier), `GPT-5-mini` class, large `Qwen` / `DeepSeek` class |
 | `opus` | Frontier reasoning; critical or complex work | whatever the provider sells as its extended / deliberate-reasoning tier — currently `GPT-5.5`, deep-think modes, `Kimi K3` class, any model whose advantage is longer deliberation rather than throughput |
+| `fable` | Ceiling; reached only by escalation or explicit request | Anthropic's Claude Fable, the tier above Opus. On another provider, the deliberate-reasoning edition it sells *above* its `opus`-class model (`-pro`, `-ultra`, deep-think variants); if the provider has no such tier, map `fable` to the same model as `opus` and the ladder ends there |
 
 The mapping is by **capability tier, not by name** — exact names drift as vendors ship new models. Every rule above is expressed in tiers, so on another provider: map tier → your model of that class, then apply the selection, weighting, pairing and escalation rules unchanged.
 
@@ -783,7 +784,7 @@ Each step has an implementation model. Each **phase** additionally has a **revie
 - Take the HIGHEST implementation tier in the phase as the baseline, then decide whether to go one tier up.
 - Go one tier up (the usual case) when the phase mixes concerns, crosses a contract, or its checklist items are the essential ones.
 - Stay at the same tier when the phase is small, uniform and mechanical and the higher tier would add nothing — e.g. a phase of two `sonnet` steps that both apply one established pattern may keep `sonnet`.
-- `opus` is the ceiling; a phase containing an `opus` step is reviewed by `opus`.
+- `opus` is the highest tier this rule assigns; a phase containing an `opus` step is reviewed by `opus`. `fable` is not pre-assigned as a reviewer — implementation-time escalation reaches it when an `opus` review lets a structural defect through.
 - Never review below the highest implementation tier used in the phase.
 
 ##### Common Mistakes to AVOID
@@ -794,6 +795,7 @@ Each step has an implementation model. Each **phase** additionally has a **revie
 | `developer` for writing README | README is documentation | `tech-writer` |
 | `opus` "to be safe" when unsure | `opus` must be EARNED by a breadth/critical/open-design trigger — uncertainty is not a trigger | `sonnet` (the tie-breaker default); escalate later if the step turns out to need it |
 | `opus` for ordinary feature/fix/refactor work | Local design choices on an established pattern are exactly what `sonnet` is for | `sonnet` |
+| `fable` pre-assigned to a step or reviewer | `fable` is the escalation ceiling, not a planning tier — a plan never spends it before `opus` has failed | `opus` (if earned); implementation escalates to `fable` when an `opus` attempt fails |
 | `haiku` for anything requiring judgment | Haiku is for mechanical tasks with no decisions | `sonnet` — jump straight to `opus` only if a breadth/critical/open-design trigger also fires |
 | `code-explorer` for fixing bugs | Explorer analyzes, doesn't implement | `developer` |
 | `researcher` for writing code | Researcher defines skills, doesn't code | `developer` |
@@ -876,7 +878,7 @@ Write each step to its own file using this template. It is the step template —
 
 **Task File:** `.specs/tasks/todo/<task-name>.md`
 **Phase:** Phase N
-**Model:** [Model type - haiku/sonnet/opus]
+**Model:** [Model type - haiku/sonnet/opus/fable]
 **Agent:** [Agent type - see Agent Selection Guide]
 **Depends on:** [List of step names, or "None"]
 **Parallel with:** [List of step names that share same dependencies, or "None"]
@@ -1045,7 +1047,7 @@ Step 02a-...      Step 02b-...      Step 02c-...
 #### Phase 1
 
 Steps: `<step-1-name>`, `<step-2-name>`, ...
-Reviewer model: `<haiku|sonnet|opus>`
+Reviewer model: `<haiku|sonnet|opus|fable>`
 Acceptance Criteria that should be fulfiled:
 Checklist items:
 - `<checklist-item-1>`
@@ -1060,7 +1062,7 @@ Rubrics:
 #### Phase 2
 
 Steps: `<step-1-name>`, `<step-2-name>`, ...
-Reviewer model: `<haiku|sonnet|opus>`
+Reviewer model: `<haiku|sonnet|opus|fable>`
 Acceptance Criteria that should be fulfiled:
 Checklist items:
 - `<checklist-item-1>`
@@ -1077,7 +1079,7 @@ Rubrics:
 
 - The phase identifier is `Phase N`. You MAY append a short title after it (`#### Phase 1: Foundation`); the identifier must remain parseable as `Phase N`.
 - `Steps:` lists step names — the sub-task file basenames without `.md` — in execution order, backtick-quoted and comma-separated.
-- `Reviewer model:` is exactly one of `haiku`, `sonnet`, `opus`.
+- `Reviewer model:` is exactly one of `haiku`, `sonnet`, `opus`, `fable`.
 - Checklist items are cited by ID plus a short quote of the question, e.g. ``- `CK-3` — Does every public endpoint reject unauthenticated requests?``
 - Rubrics are cited by criterion name exactly as written in the `**Rubric:**` table, e.g. ``- `Project Guidelines Alignment` ``.
 - If a phase has no rubric criteria due yet, write `Rubrics:` followed by `- None`. Never omit the heading.

antigravity/agents/tech-lead.md

@@ -31,7 +31,7 @@ Use a scratchpad-first approach: think deeply and analyze everything in a scratc
 
 - **Task File**: Path to the task file (e.g., `.specs/tasks/draft/<task-name>.md`)
   - Contains: Initial User Prompt, Description, Acceptance Criteria, Architecture Overview
-- **Available agents** (optional): the launch prompt MAY list the agents available in this project (e.g. `sdd:developer`, `review:bug-hunter`, plus the general agents `opus`, `sonnet`, `haiku`). If it does, you MUST use ONLY agents from that list. If it does not, use the [Agent Selection Guide](#agent-selection-guide) below.
+- **Available agents** (optional): the launch prompt MAY list the agents available in this project (e.g. `sdd:developer`, `review:bug-hunter`, plus the general agents `fable`, `opus`, `sonnet`, `haiku`). If it does, you MUST use ONLY agents from that list. If it does not, use the [Agent Selection Guide](#agent-selection-guide) below.
 - **Model Selection Policy** (optional): the launch prompt MAY paste a per-step model tier policy. If it does, apply it. If it does not, use the [Model Selection Guide](#model-selection-guide) below.
 
 ## CRITICAL: Load Context
@@ -745,7 +745,7 @@ Model choice is not a formality — it is the single biggest factor in whether a
 
 **Selection Rules**
 
-**Tier default:** `sonnet`/`haiku` cover the majority of steps. `opus` is reserved and opt-in — it MUST be *earned* by a trigger in the table below, never picked because you are unsure or "to be safe."
+**Tier default:** `sonnet`/`haiku` cover the majority of steps. `opus` is reserved and opt-in — it MUST be *earned* by a trigger in the table below, never picked because you are unsure or "to be safe." `fable` sits above `opus` and is never pre-assigned to a step or a reviewer: no row below selects it. It is reserved for implementation-time escalation after `opus` has failed, or for an explicit `--model fable`.
 
 | Step shape | Tier | Examples |
 |---|---|---|
@@ -766,6 +766,7 @@ When this skill runs outside the Anthropic model context, map the tier to the ne
 | `haiku` | Fast and cheap; mechanical work | `gemini-flash-lite`, `gemma` class, `gpt-oss` class, small open-weight models |
 | `sonnet` | Balanced workhorse; most planning phases | `gemini-pro` class and full `gemini-flash` (**not** the `-lite` variant, which is `haiku`-tier), `GPT-5-mini` class, large `Qwen` / `DeepSeek` class |
 | `opus` | Frontier reasoning; critical or complex work | whatever the provider sells as its extended / deliberate-reasoning tier — currently `GPT-5.5`, deep-think modes, `Kimi K3` class, any model whose advantage is longer deliberation rather than throughput |
+| `fable` | Ceiling; reached only by escalation or explicit request | Anthropic's Claude Fable, the tier above Opus. On another provider, the deliberate-reasoning edition it sells *above* its `opus`-class model (`-pro`, `-ultra`, deep-think variants); if the provider has no such tier, map `fable` to the same model as `opus` and the ladder ends there |
 
 The mapping is by **capability tier, not by name** — exact names drift as vendors ship new models. Every rule above is expressed in tiers, so on another provider: map tier → your model of that class, then apply the selection, weighting, pairing and escalation rules unchanged.
 
@@ -787,7 +788,7 @@ Each step has an implementation model. Each **phase** additionally has a **revie
 - Take the HIGHEST implementation tier in the phase as the baseline, then decide whether to go one tier up.
 - Go one tier up (the usual case) when the phase mixes concerns, crosses a contract, or its checklist items are the essential ones.
 - Stay at the same tier when the phase is small, uniform and mechanical and the higher tier would add nothing — e.g. a phase of two `sonnet` steps that both apply one established pattern may keep `sonnet`.
-- `opus` is the ceiling; a phase containing an `opus` step is reviewed by `opus`.
+- `opus` is the highest tier this rule assigns; a phase containing an `opus` step is reviewed by `opus`. `fable` is not pre-assigned as a reviewer — implementation-time escalation reaches it when an `opus` review lets a structural defect through.
 - Never review below the highest implementation tier used in the phase.
 
 ##### Common Mistakes to AVOID
@@ -798,6 +799,7 @@ Each step has an implementation model. Each **phase** additionally has a **revie
 | `developer` for writing README | README is documentation | `tech-writer` |
 | `opus` "to be safe" when unsure | `opus` must be EARNED by a breadth/critical/open-design trigger — uncertainty is not a trigger | `sonnet` (the tie-breaker default); escalate later if the step turns out to need it |
 | `opus` for ordinary feature/fix/refactor work | Local design choices on an established pattern are exactly what `sonnet` is for | `sonnet` |
+| `fable` pre-assigned to a step or reviewer | `fable` is the escalation ceiling, not a planning tier — a plan never spends it before `opus` has failed | `opus` (if earned); implementation escalates to `fable` when an `opus` attempt fails |
 | `haiku` for anything requiring judgment | Haiku is for mechanical tasks with no decisions | `sonnet` — jump straight to `opus` only if a breadth/critical/open-design trigger also fires |
 | `code-explorer` for fixing bugs | Explorer analyzes, doesn't implement | `developer` |
 | `researcher` for writing code | Researcher defines skills, doesn't code | `developer` |
@@ -880,7 +882,7 @@ Write each step to its own file using this template. It is the step template —
 
 **Task File:** `.specs/tasks/todo/<task-name>.md`
 **Phase:** Phase N
-**Model:** [Model type - haiku/sonnet/opus]
+**Model:** [Model type - haiku/sonnet/opus/fable]
 **Agent:** [Agent type - see Agent Selection Guide]
 **Depends on:** [List of step names, or "None"]
 **Parallel with:** [List of step names that share same dependencies, or "None"]
@@ -1049,7 +1051,7 @@ Step 02a-...      Step 02b-...      Step 02c-...
 #### Phase 1
 
 Steps: `<step-1-name>`, `<step-2-name>`, ...
-Reviewer model: `<haiku|sonnet|opus>`
+Reviewer model: `<haiku|sonnet|opus|fable>`
 Acceptance Criteria that should be fulfiled:
 Checklist items:
 - `<checklist-item-1>`
@@ -1064,7 +1066,7 @@ Rubrics:
 #### Phase 2
 
 Steps: `<step-1-name>`, `<step-2-name>`, ...
-Reviewer model: `<haiku|sonnet|opus>`
+Reviewer model: `<haiku|sonnet|opus|fable>`
 Acceptance Criteria that should be fulfiled:
 Checklist items:
 - `<checklist-item-1>`
@@ -1081,7 +1083,7 @@ Rubrics:
 
 - The phase identifier is `Phase N`. You MAY append a short title after it (`#### Phase 1: Foundation`); the identifier must remain parseable as `Phase N`.
 - `Steps:` lists step names — the sub-task file basenames without `.md` — in execution order, backtick-quoted and comma-separated.
-- `Reviewer model:` is exactly one of `haiku`, `sonnet`, `opus`.
+- `Reviewer model:` is exactly one of `haiku`, `sonnet`, `opus`, `fable`.
 - Checklist items are cited by ID plus a short quote of the question, e.g. ``- `CK-3` — Does every public endpoint reject unauthenticated requests?``
 - Rubrics are cited by criterion name exactly as written in the `**Rubric:**` table, e.g. ``- `Project Guidelines Alignment` ``.
 - If a phase has no rubric criteria due yet, write `Rubrics:` followed by `- None`. Never omit the heading.

antigravity/skills/implement-task/SKILL.md

@@ -42,7 +42,7 @@ Parse the following arguments from `$ARGUMENTS`:
 | `--target-quality` | `--target-quality X.X` | `4.0` | Single target threshold value (out of 5.0) applied to every implementation phase review. |
 | `--max-iterations` | `--max-iterations N` | `3` | Maximum fix→re-review cycles per implementation phase. Default is 3 iterations. Set to `unlimited` for no limit. |
 | `--skip-reviews` | `--skip-reviews` | `false` | Skip all phase reviews - steps proceed without quality gates. |
-| `--model` | `opus\|sonnet\|haiku` | Unset | Model for **all** sub-agents (implementation agents AND `sdd:code-reviewer`) that **overrides** every model in the task file; when omitted, step models come from the Parallelization Overview and reviewer models from the Phase Overview. |
+| `--model` | `fable\|opus\|sonnet\|haiku` | Unset | Model for **all** sub-agents (implementation agents AND `sdd:code-reviewer`) that **overrides** every model in the task file; when omitted, step models come from the Parallelization Overview and reviewer models from the Phase Overview. |
 | `--strict` | `--strict` | `false` | Disable the [Iteration Discretion Rule](#iteration-discretion-rule) - a phase is marked PASS ONLY when `combined_score >= THRESHOLD`, otherwise iterate until `MAX_ITERATIONS` is reached. |
 
 ### Configuration Resolution
@@ -57,7 +57,7 @@ TASK_FILE = first argument that is a file path or filename
 THRESHOLD = --target-quality value || 4.0
 
 # Initialize other defaults
-MODEL_OVERRIDE = --model value (opus|sonnet|haiku) || none  # none = no override; models come from the task file
+MODEL_OVERRIDE = --model value (fable|opus|sonnet|haiku) || none  # none = no override; models come from the task file
 MAX_ITERATIONS = --max-iterations || 3  # default is 3 iterations
 HUMAN_IN_THE_LOOP_PHASES = --human-in-the-loop || [] (empty = none, "*" = all implementation phases)
 SKIP_REVIEWS = --skip-reviews || false
@@ -784,7 +784,7 @@ Before dispatching a single fix, reason **explicitly and in writing** through:
 2. **Depth** — is this a local defect inside a step, or did the phase come out structurally wrong (`blast_radius.requires_phase_rework`)?
 3. **Coupling** — does fixing the affected steps force rewriting the unaffected ones? If yes, the unit of repair is the phase, not the step.
 4. **Severity** — High/Critical findings that break an acceptance criterion the phase owns, or Low/Medium nitpicks?
-5. **Ceiling** — does the failure look like the implementing model ran out of capability? If a model already failed once on the same finding, dispatching it again at the same tier will fail again. Escalate.
+5. **Ceiling** — does the failure look like the implementing model ran out of capability? If a model already failed once on the same finding, dispatching it again at the same tier will fail again. Escalate. The ladder is `haiku` → `sonnet` → `opus` → `fable`; `fable` is the last rung, so work that has already failed at `fable` goes back to the user, not to another dispatch.
 
 Then decide three things:
 
@@ -1635,7 +1635,7 @@ Rubrics:
 ```
 
 - The **phase identifier** is `Phase N` (a title may follow: `#### Phase 1: Foundation`). This exact identifier is what you pass to the reviewer.
-- `Reviewer model:` is one of `haiku`, `sonnet`, `opus`. It is the model of that phase's single review dispatch.
+- `Reviewer model:` is one of `haiku`, `sonnet`, `opus`, `fable`. It is the model of that phase's single review dispatch.
 - The `Checklist items:` and `Rubrics:` lists scope the reviewer's scoring. **They are the reviewer's input, not yours** — it reads them from the task file itself. Never paste them into a prompt.
 
 ### Sub-Task Files
@@ -1647,7 +1647,7 @@ One per step, at `.specs/sub-tasks/<task-name>/<NN>-<step-slug>.md`, where `<tas
 
 **Task File:** `.specs/tasks/todo/<task-name>.md`
 **Phase:** Phase N
-**Model:** haiku | sonnet | opus
+**Model:** haiku | sonnet | opus | fable
 **Agent:** [agent type]
 **Depends on:** [step names or None]
 **Parallel with:** [step names or None]