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.test.ts

@@ -13,17 +13,49 @@ describe("model-capability-aliases", () => {
     })
   })
 
-  test("normalizes exact local tier aliases to canonical models.dev IDs", () => {
+  test("strips provider prefixes when the input is already canonical", () => {
+    const result = resolveModelIDAlias("anthropic/claude-sonnet-4-6")
+
+    expect(result).toEqual({
+      requestedModelID: "anthropic/claude-sonnet-4-6",
+      canonicalModelID: "claude-sonnet-4-6",
+      source: "canonical",
+    })
+  })
+
+  test("normalizes gemini tier aliases through a pattern rule", () => {
     const result = resolveModelIDAlias("gemini-3.1-pro-high")
 
     expect(result).toEqual({
       requestedModelID: "gemini-3.1-pro-high",
       canonicalModelID: "gemini-3.1-pro",
-      source: "exact-alias",
+      source: "pattern-alias",
       ruleID: "gemini-3.1-pro-tier-alias",
     })
   })
 
+  test("normalizes provider-prefixed gemini tier aliases to bare canonical IDs", () => {
+    const result = resolveModelIDAlias("google/gemini-3.1-pro-high")
+
+    expect(result).toEqual({
+      requestedModelID: "google/gemini-3.1-pro-high",
+      canonicalModelID: "gemini-3.1-pro",
+      source: "pattern-alias",
+      ruleID: "gemini-3.1-pro-tier-alias",
+    })
+  })
+
+  test("keeps exceptional gemini preview aliases as exact rules", () => {
+    const result = resolveModelIDAlias("gemini-3-pro-high")
+
+    expect(result).toEqual({
+      requestedModelID: "gemini-3-pro-high",
+      canonicalModelID: "gemini-3-pro-preview",
+      source: "exact-alias",
+      ruleID: "gemini-3-pro-tier-alias",
+    })
+  })
+
   test("does not resolve prototype keys as aliases", () => {
     const result = resolveModelIDAlias("constructor")
 
@@ -34,14 +66,45 @@ describe("model-capability-aliases", () => {
     })
   })
 
-  test("normalizes legacy Claude thinking aliases through a named exact rule", () => {
+  test("normalizes provider-prefixed Claude thinking aliases through a pattern rule", () => {
+    const result = resolveModelIDAlias("anthropic/claude-opus-4-6-thinking")
+
+    expect(result).toEqual({
+      requestedModelID: "anthropic/claude-opus-4-6-thinking",
+      canonicalModelID: "claude-opus-4-6",
+      source: "pattern-alias",
+      ruleID: "claude-thinking-legacy-alias",
+    })
+  })
+
+  test("does not pattern-match nearby canonical Claude IDs incorrectly", () => {
+    const result = resolveModelIDAlias("claude-opus-4-6-think")
+
+    expect(result).toEqual({
+      requestedModelID: "claude-opus-4-6-think",
+      canonicalModelID: "claude-opus-4-6-think",
+      source: "canonical",
+    })
+  })
+
+  test("does not pattern-match canonical gemini preview IDs incorrectly", () => {
+    const result = resolveModelIDAlias("gemini-3.1-pro-preview")
+
+    expect(result).toEqual({
+      requestedModelID: "gemini-3.1-pro-preview",
+      canonicalModelID: "gemini-3.1-pro-preview",
+      source: "canonical",
+    })
+  })
+
+  test("normalizes legacy Claude thinking aliases through a pattern rule", () => {
     const result = resolveModelIDAlias("claude-opus-4-6-thinking")
 
     expect(result).toEqual({
       requestedModelID: "claude-opus-4-6-thinking",
       canonicalModelID: "claude-opus-4-6",
-      source: "exact-alias",
-      ruleID: "claude-opus-4-6-thinking-legacy-alias",
+      source: "pattern-alias",
+      ruleID: "claude-thinking-legacy-alias",
     })
   })
 })