feat(coder): add model resolution core + multi-batch matcher

Model resolution (from oh-my-openagent/model-core): 6-step priority
resolution pipeline (UI select -> user config -> category default ->
user fallback -> policy chain -> system default), provider fallback
chains, fuzzy model matching, error classification, provider-specific
model ID transforms. 14 files, zero runtime deps.

Multi-batch matcher (from boocontext-audit): 6 batch types
(Observational, Actionable, PreviouslyApplied, Disambiguation,
ResponseAnalysis, LowCriticality) for behavioral guideline evaluation.
RelationalResolver with iterative convergence (DEPENDS_ON,
PRIORITIZES, ENTAILS, TAG_ALL, TAG_PRIORITIZES). SchematicGenerator
abstract class with retry and execution plans. 4 files.

apps/coder/src/services/model-resolution/model-resolver.ts

@@ -0,0 +1,109 @@
+import type { FallbackEntry } from "./model-requirement-types.js"
+import type { FallbackModelObject } from "./fallback-model-object.js"
+import { normalizeModel } from "./model-normalization.js"
+import { resolveModelPipeline } from "./model-resolution-pipeline.js"
+import { KNOWN_VARIANTS } from "./known-variants.js"
+import type { ConnectedProvidersAdapter } from "./connected-providers-cache.js"
+import * as connectedProvidersCache from "./connected-providers-cache.js"
+
+export type ModelResolutionInput = {
+  userModel?: string
+  inheritedModel?: string
+  systemDefault?: string
+}
+
+export type ModelSource =
+  | "override"
+  | "category-default"
+  | "provider-fallback"
+  | "system-default"
+
+export type ModelResolutionResult = {
+  model: string
+  source: ModelSource
+  variant?: string
+}
+
+export type ExtendedModelResolutionInput = {
+  uiSelectedModel?: string
+  userModel?: string
+  userFallbackModels?: string[]
+  categoryDefaultModel?: string
+  fallbackChain?: FallbackEntry[]
+  availableModels: Set<string>
+  systemDefaultModel?: string
+}
+
+
+export function resolveModel(input: ModelResolutionInput): string | undefined {
+  return (
+    normalizeModel(input.userModel) ??
+    normalizeModel(input.inheritedModel) ??
+    input.systemDefault
+  )
+}
+
+export function resolveModelWithFallback(
+  input: ExtendedModelResolutionInput,
+  connectedProvidersAdapter: ConnectedProvidersAdapter = connectedProvidersCache,
+): ModelResolutionResult | undefined {
+  const { uiSelectedModel, userModel, userFallbackModels, categoryDefaultModel, fallbackChain, availableModels, systemDefaultModel } = input
+  const resolved = resolveModelPipeline({
+    intent: { uiSelectedModel, userModel, userFallbackModels, categoryDefaultModel },
+    constraints: { availableModels },
+    policy: { fallbackChain, systemDefaultModel },
+  }, connectedProvidersAdapter)
+
+  if (!resolved) {
+    return undefined
+  }
+
+  return {
+    model: resolved.model,
+    source: resolved.provenance,
+    variant: resolved.variant,
+  }
+}
+
+/**
+ * Normalizes fallback_models config to a mixed array.
+ * Accepts string, string[], or mixed arrays of strings and FallbackModelObject entries.
+ */
+export function normalizeFallbackModels(
+  models: string | (string | FallbackModelObject)[] | undefined,
+): (string | FallbackModelObject)[] | undefined {
+  if (!models) return undefined
+  if (typeof models === "string") return [models]
+  return models
+}
+
+/**
+ * Extracts plain model strings from a mixed fallback models array.
+ * Object entries are flattened to "model" or "model(variant)" strings.
+ * Use this when consumers need string[] (e.g., resolveModelForDelegateTask).
+ */
+export function flattenToFallbackModelStrings(
+  models: (string | FallbackModelObject)[] | undefined,
+): string[] | undefined {
+  if (!models) return undefined
+  return models.map((entry) => {
+    if (typeof entry === "string") return entry
+    const variant = entry.variant
+    if (variant) {
+      // Strip any supported inline variant syntax before appending explicit override.
+      // Supports both parenthesized and space-suffix forms so we don't emit
+      // invalid strings like "provider/model high(low)".
+      const model = entry.model
+        .replace(/\([^()]+\)\s*$/, "")
+        .replace(/\s+([a-z][a-z0-9_-]*)\s*$/i, (_match: string, suffix: string) => {
+          const normalized = String(suffix).toLowerCase()
+          return KNOWN_VARIANTS.has(normalized)
+            ? ""
+            : _match
+        })
+        .trim()
+      return `${model}(${variant})`
+    }
+    return entry.model
+  })
+}