feat: model taxonomy gains gpt-5.6-sol + per-host generation defaults

Adds 'gpt-5.6-sol' to the model taxonomy with exact-match-only resolution
(Terra/Luna/suffixed IDs deliberately fall back to generic gpt) and replaces
the hardcoded 'claude' generation default with a validated
HostConfig.defaultModel: codex renders the gpt profile when --model is
absent, every other host keeps claude. Codex ship golden regenerated
accordingly; ADDING_A_HOST documents the new field.

scripts/gen-skill-docs.ts

@@ -92,12 +92,13 @@ const HOST_ARG_VAL: HostArg = (() => {
 let HOST: Host = HOST_ARG_VAL === 'all' ? 'claude' : HOST_ARG_VAL;
 
 // ─── Model Overlay Selection ────────────────────────────────
-// --model is explicit. We do NOT auto-detect from host (host ≠ model).
-// Default is 'claude'. Missing overlay file → empty string (graceful).
+// --model is explicit. Without it, each host uses HostConfig.defaultModel.
+// Host defaults are generation fallbacks, not claims that host === model.
+// Missing overlay file → empty string (graceful).
 import { ALL_MODEL_NAMES, resolveModel, type Model } from './models';
 const MODEL_ARG = process.argv.find(a => a.startsWith('--model'));
-const MODEL_ARG_VAL: Model = (() => {
-  if (!MODEL_ARG) return 'claude';
+const MODEL_ARG_VAL: Model | null = (() => {
+  if (!MODEL_ARG) return null;
   const val = MODEL_ARG.includes('=') ? MODEL_ARG.split('=')[1] : process.argv[process.argv.indexOf(MODEL_ARG) + 1];
   const resolved = resolveModel(val);
   if (!resolved) {
@@ -106,6 +107,10 @@ const MODEL_ARG_VAL: Model = (() => {
   return resolved;
 })();
 
+function generationModelForHost(host: Host): Model {
+  return MODEL_ARG_VAL ?? getHostConfig(host).defaultModel;
+}
+
 // ─── Catalog Mode (v1.45.0.0 T4) ────────────────────────────
 // 'trim' (default): shorten frontmatter description to lead sentence and
 // move routing/voice prose into a "## When to invoke" body section.
@@ -753,7 +758,7 @@ function buildContext(
   const interactive = interactiveMatch ? interactiveMatch[1] === 'true' : undefined;
   return {
     skillName, tmplPath, benefitsFrom, host, paths: HOST_PATHS[host],
-    preambleTier, model: MODEL_ARG_VAL, interactive, explainLevel: EXPLAIN_LEVEL,
+    preambleTier, model: generationModelForHost(host), interactive, explainLevel: EXPLAIN_LEVEL,
   };
 }
 

scripts/host-config.ts

@@ -14,6 +14,9 @@
  *                                              platform-detect, uninstall
  */
 
+import type { Model } from './models';
+import { validateModel } from './models';
+
 export interface HostConfig {
   /** Unique host identifier (e.g., 'opencode'). Must match filename in hosts/. */
   name: string;
@@ -24,6 +27,9 @@ export interface HostConfig {
   /** Alternative binary names (e.g., ['droid'] for factory). */
   cliAliases?: string[];
 
+  /** Model overlay used when generation does not receive an explicit --model. */
+  defaultModel: Model;
+
   // --- Path Configuration ---
   /** Global install path relative to $HOME (e.g., '.config/opencode/skills/gstack'). */
   globalRoot: string;
@@ -119,6 +125,10 @@ export function validateHostConfig(config: HostConfig, validResolverNames?: Read
       }
     }
   }
+  const modelError = validateModel(config.defaultModel);
+  if (modelError) {
+    errors.push(`defaultModel ${modelError}`);
+  }
   if (!PATH_REGEX.test(config.globalRoot)) {
     errors.push(`globalRoot '${config.globalRoot}' contains invalid characters`);
   }

scripts/models.ts

@@ -2,13 +2,17 @@
  * Model taxonomy — neutral module with no imports from hosts/ or resolvers/.
  *
  * Model families supported by model overlays in model-overlays/{family}.md.
- * Host configs can reference these as `defaultModel` strings (validated at
+ * Host configs reference these as `defaultModel` strings (validated at
  * generation time), but the model axis is independent of the host axis.
  *
  * IMPORTANT: host ≠ model. Claude Code can run any Claude model (Opus, Sonnet,
  * Haiku, future). Codex CLI runs GPT/o-series models. Cursor and OpenCode can
- * front multiple providers. We do NOT auto-detect the model from the host —
- * users pass --model explicitly. Default is 'claude'.
+ * front multiple providers. The generator does NOT auto-detect the model from
+ * the host — users can pass --model explicitly, otherwise each host supplies
+ * its own generation default. Exception outside this module: ./setup detects
+ * the Codex model from ${CODEX_HOME:-~/.codex}/config.toml
+ * (scripts/resolve-codex-generation-model.ts) and passes it as an explicit
+ * --model.
  */
 
 export const ALL_MODEL_NAMES = [
@@ -19,6 +23,7 @@ export const ALL_MODEL_NAMES = [
   'sonnet-5',
   'gpt',
   'gpt-5.4',
+  'gpt-5.6-sol',
   'gemini',
   'o-series',
 ] as const;
@@ -29,10 +34,11 @@ export type Model = (typeof ALL_MODEL_NAMES)[number];
  * Resolve a model argument from CLI input to a known Model family.
  *
  * Precedence rules:
- * 1. Exact match against ALL_MODEL_NAMES → return as-is.
+ * 1. Exact match against ALL_MODEL_NAMES → return as-is. This is the ONLY
+ *    path that selects `gpt-5.6-sol` — Sol is intentionally exact-only.
  * 2. Family heuristics for common variants:
  *    - `gpt-5.4-mini`, `gpt-5.4-turbo`, `gpt-5.4-*` → `gpt-5.4`
- *    - `gpt-*` (anything else GPT) → `gpt`
+ *    - `gpt-*` (anything else GPT, including other 5.6 variants) → `gpt`
  *    - `o3`, `o4`, `o4-mini`, `o1`, `o1-mini`, `o1-pro` → `o-series`
  *    - `claude-*` (sonnet, opus, haiku, any version) → `claude`
  *    - `gemini-*` (2.5-pro, flash, etc.) → `gemini`
@@ -52,6 +58,10 @@ export function resolveModel(input: string): Model | null {
   }
 
   // Family heuristics
+  // Sol never reaches here — the exact match above already returned it. Do
+  // not add a Sol family pattern: Terra, Luna, future 5.6 variants, and
+  // suffixed model IDs must NOT inherit Sol's behavioral profile; they fall
+  // through to the generic `gpt` family below.
   if (/^gpt-5\.4(-|$)/.test(s)) return 'gpt-5.4';
   if (/^gpt(-|$)/.test(s)) return 'gpt';
   if (/^o[0-9]+(-|$)/.test(s)) return 'o-series';