refactor(aliases): migrate to pattern-based model alias resolution

Move from hardcoded exact aliases to pattern-based canonicalization:

- Populate PATTERN_ALIAS_RULES with regex patterns for:
  - Claude thinking variants (claude-opus-4-6-thinking → claude-opus-4-6)
  - Gemini tier suffixes (gemini-3.1-pro-{high,low} → gemini-3.1-pro)
- Add stripProviderPrefixForAliasLookup() for provider-prefixed models
  (anthropic/claude-sonnet-4-6 → claude-sonnet-4-6 for capability lookup)
- Preserve requestedModelID (with prefix) for API transport
- Reduce EXACT_ALIAS_RULES to exceptional cases only
  (gemini-3-pro-{high,low} → gemini-3-pro-preview)
- Comprehensive test coverage for patterns, prefix stripping, negatives

Addresses Discussion #2835 (pattern matching architecture)
Related to PR #2834 (alias guardrails)

41 targeted tests pass, 4467 full suite tests pass, tsc clean.

src/shared/model-capability-aliases.ts

@@ -20,18 +20,6 @@ export type ModelIDAliasResolution = {
 }
 
 const EXACT_ALIAS_RULES: ReadonlyArray<ExactAliasRule> = [
-  {
-    aliasModelID: "gemini-3.1-pro-high",
-    ruleID: "gemini-3.1-pro-tier-alias",
-    canonicalModelID: "gemini-3.1-pro",
-    rationale: "OmO historically encoded Gemini tier selection in the model name instead of variant metadata.",
-  },
-  {
-    aliasModelID: "gemini-3.1-pro-low",
-    ruleID: "gemini-3.1-pro-tier-alias",
-    canonicalModelID: "gemini-3.1-pro",
-    rationale: "OmO historically encoded Gemini tier selection in the model name instead of variant metadata.",
-  },
   {
     aliasModelID: "gemini-3-pro-high",
     ruleID: "gemini-3-pro-tier-alias",
@@ -44,30 +32,47 @@ const EXACT_ALIAS_RULES: ReadonlyArray<ExactAliasRule> = [
     canonicalModelID: "gemini-3-pro-preview",
     rationale: "Legacy Gemini 3 tier suffixes still need to land on the canonical preview model.",
   },
-  {
-    aliasModelID: "claude-opus-4-6-thinking",
-    ruleID: "claude-opus-4-6-thinking-legacy-alias",
-    canonicalModelID: "claude-opus-4-6",
-    rationale: "OmO historically used a legacy compatibility suffix before models.dev shipped canonical thinking variants for newer Claude families.",
-  },
 ]
 
 const EXACT_ALIAS_RULES_BY_MODEL: ReadonlyMap<string, ExactAliasRule> = new Map(
   EXACT_ALIAS_RULES.map((rule) => [rule.aliasModelID, rule]),
 )
 
-const PATTERN_ALIAS_RULES: ReadonlyArray<PatternAliasRule> = []
+const PATTERN_ALIAS_RULES: ReadonlyArray<PatternAliasRule> = [
+  {
+    ruleID: "claude-thinking-legacy-alias",
+    description: "Normalizes the legacy Claude Opus 4.6 thinking suffix to the canonical snapshot ID.",
+    match: (normalizedModelID) => /^claude-opus-4-6-thinking$/.test(normalizedModelID),
+    canonicalize: () => "claude-opus-4-6",
+  },
+  {
+    ruleID: "gemini-3.1-pro-tier-alias",
+    description: "Normalizes Gemini 3.1 Pro tier suffixes to the canonical snapshot ID.",
+    match: (normalizedModelID) => /^gemini-3\.1-pro-(?:high|low)$/.test(normalizedModelID),
+    canonicalize: () => "gemini-3.1-pro",
+  },
+]
 
 function normalizeLookupModelID(modelID: string): string {
   return modelID.trim().toLowerCase()
 }
 
+function stripProviderPrefixForAliasLookup(normalizedModelID: string): string {
+  const slashIndex = normalizedModelID.indexOf("/")
+  if (slashIndex <= 0 || slashIndex === normalizedModelID.length - 1) {
+    return normalizedModelID
+  }
+
+  return normalizedModelID.slice(slashIndex + 1)
+}
+
 export function resolveModelIDAlias(modelID: string): ModelIDAliasResolution {
-  const normalizedModelID = normalizeLookupModelID(modelID)
-  const exactRule = EXACT_ALIAS_RULES_BY_MODEL.get(normalizedModelID)
+  const requestedModelID = normalizeLookupModelID(modelID)
+  const aliasLookupModelID = stripProviderPrefixForAliasLookup(requestedModelID)
+  const exactRule = EXACT_ALIAS_RULES_BY_MODEL.get(aliasLookupModelID)
   if (exactRule) {
     return {
-      requestedModelID: normalizedModelID,
+      requestedModelID,
       canonicalModelID: exactRule.canonicalModelID,
       source: "exact-alias",
       ruleID: exactRule.ruleID,
@@ -75,21 +80,21 @@ export function resolveModelIDAlias(modelID: string): ModelIDAliasResolution {
   }
 
   for (const rule of PATTERN_ALIAS_RULES) {
-    if (!rule.match(normalizedModelID)) {
+    if (!rule.match(aliasLookupModelID)) {
       continue
     }
 
     return {
-      requestedModelID: normalizedModelID,
-      canonicalModelID: rule.canonicalize(normalizedModelID),
+      requestedModelID,
+      canonicalModelID: rule.canonicalize(aliasLookupModelID),
       source: "pattern-alias",
       ruleID: rule.ruleID,
     }
   }
 
   return {
-    requestedModelID: normalizedModelID,
-    canonicalModelID: normalizedModelID,
+    requestedModelID,
+    canonicalModelID: aliasLookupModelID,
     source: "canonical",
   }
 }