refactor(shared): split model-availability.ts into model resolution modules

Extract model availability checking pipeline:
- available-models-fetcher.ts: top-level model fetching orchestration
- model-cache-availability.ts, models-json-cache-reader.ts
- provider-models-cache-model-reader.ts: provider cache reading with null guard
- fallback-model-availability.ts, model-name-matcher.ts
- open-code-client-accessors.ts, open-code-client-shapes.ts
- record-type-guard.ts

src/shared/model-name-matcher.ts

@@ -0,0 +1,91 @@
+import { log } from "./logger"
+
+function normalizeModelName(name: string): string {
+	return name
+		.toLowerCase()
+		.replace(/claude-(opus|sonnet|haiku)-4-5/g, "claude-$1-4.5")
+		.replace(/claude-(opus|sonnet|haiku)-4\.5/g, "claude-$1-4.5")
+}
+
+export function fuzzyMatchModel(
+	target: string,
+	available: Set<string>,
+	providers?: string[],
+): string | null {
+	log("[fuzzyMatchModel] called", { target, availableCount: available.size, providers })
+
+	if (available.size === 0) {
+		log("[fuzzyMatchModel] empty available set")
+		return null
+	}
+
+	const targetNormalized = normalizeModelName(target)
+
+	let candidates = Array.from(available)
+	if (providers && providers.length > 0) {
+		const providerSet = new Set(providers)
+		candidates = candidates.filter((model) => {
+			const [provider] = model.split("/")
+			return providerSet.has(provider)
+		})
+		log("[fuzzyMatchModel] filtered by providers", {
+			candidateCount: candidates.length,
+			candidates: candidates.slice(0, 10),
+		})
+	}
+
+	if (candidates.length === 0) {
+		log("[fuzzyMatchModel] no candidates after filter")
+		return null
+	}
+
+	const matches = candidates.filter((model) =>
+		normalizeModelName(model).includes(targetNormalized),
+	)
+
+	log("[fuzzyMatchModel] substring matches", {
+		targetNormalized,
+		matchCount: matches.length,
+		matches,
+	})
+
+	if (matches.length === 0) {
+		return null
+	}
+
+	const exactMatch = matches.find(
+		(model) => normalizeModelName(model) === targetNormalized,
+	)
+	if (exactMatch) {
+		log("[fuzzyMatchModel] exact match found", { exactMatch })
+		return exactMatch
+	}
+
+	const exactModelIdMatches = matches.filter((model) => {
+		const modelId = model.split("/").slice(1).join("/")
+		return normalizeModelName(modelId) === targetNormalized
+	})
+	if (exactModelIdMatches.length > 0) {
+		const result = exactModelIdMatches.reduce((shortest, current) =>
+			current.length < shortest.length ? current : shortest,
+		)
+		log("[fuzzyMatchModel] exact model ID match found", {
+			result,
+			candidateCount: exactModelIdMatches.length,
+		})
+		return result
+	}
+
+	const result = matches.reduce((shortest, current) =>
+		current.length < shortest.length ? current : shortest,
+	)
+	log("[fuzzyMatchModel] shortest match", { result })
+	return result
+}
+
+export function isModelAvailable(
+	targetModel: string,
+	availableModels: Set<string>,
+): boolean {
+	return fuzzyMatchModel(targetModel, availableModels) !== null
+}