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/fallback-chain-from-models.ts

@@ -0,0 +1,128 @@
+import type { FallbackEntry } from "./model-requirement-types.js"
+import type { FallbackModelObject } from "./fallback-model-object.js"
+import { normalizeFallbackModels } from "./model-resolver.js"
+import { KNOWN_VARIANTS } from "./known-variants.js"
+
+function parseVariantFromModel(rawModel: string): { modelID: string; variant?: string } {
+  if (typeof rawModel !== "string") {
+    return { modelID: "" }
+  }
+  const trimmedModel = rawModel.trim()
+  if (!trimmedModel) {
+    return { modelID: "" }
+  }
+
+  const parenthesizedVariant = trimmedModel.match(/^(.*)\(([^()]+)\)\s*$/)
+  if (parenthesizedVariant) {
+    const modelID = parenthesizedVariant[1]?.trim() ?? ""
+    const variant = parenthesizedVariant[2]?.trim()
+    return variant ? { modelID, variant } : { modelID }
+  }
+
+  const spaceVariant = trimmedModel.match(/^(.*\S)\s+([a-z][a-z0-9_-]*)$/i)
+  if (spaceVariant) {
+    const modelID = spaceVariant[1]?.trim() ?? ""
+    const variant = spaceVariant[2]?.trim().toLowerCase()
+    if (variant && KNOWN_VARIANTS.has(variant)) {
+      return { modelID, variant }
+    }
+  }
+
+  return { modelID: trimmedModel }
+}
+
+export function parseFallbackModelEntry(
+  model: string,
+  contextProviderID: string | undefined,
+  defaultProviderID = "opencode",
+): FallbackEntry | undefined {
+  if (typeof model !== "string") return undefined
+  const trimmed = model.trim()
+  if (!trimmed) return undefined
+
+  const parts = trimmed.split("/")
+  const providerID =
+    parts.length >= 2 ? (parts[0]?.trim() ?? "") : (contextProviderID?.trim() || defaultProviderID)
+  const rawModelID = parts.length >= 2 ? parts.slice(1).join("/").trim() : trimmed
+  if (!providerID || !rawModelID) return undefined
+
+  const parsed = parseVariantFromModel(rawModelID)
+  if (!parsed.modelID) return undefined
+
+  return {
+    providers: [providerID],
+    model: parsed.modelID,
+    variant: parsed.variant,
+  }
+}
+
+export function parseFallbackModelObjectEntry(
+  obj: FallbackModelObject,
+  contextProviderID: string | undefined,
+  defaultProviderID = "opencode",
+): FallbackEntry | undefined {
+  const base = parseFallbackModelEntry(obj.model, contextProviderID, defaultProviderID)
+  if (!base) return undefined
+
+  return {
+    ...base,
+    variant: obj.variant ?? base.variant,
+    reasoningEffort: obj.reasoningEffort,
+    temperature: obj.temperature,
+    top_p: obj.top_p,
+    maxTokens: obj.maxTokens,
+    thinking: obj.thinking,
+  }
+}
+
+/**
+ * Find the most specific FallbackEntry whose `provider/model` is a prefix of
+ * the resolved `provider/modelID`.  Longest match wins so that e.g.
+ * `openai/gpt-5.4-preview` picks the entry for `openai/gpt-5.4-preview` over
+ * the shorter `openai/gpt-5.4`.
+ */
+export function findMostSpecificFallbackEntry(
+  providerID: string,
+  modelID: string,
+  chain: FallbackEntry[],
+): FallbackEntry | undefined {
+  const resolved = `${providerID}/${modelID}`.toLowerCase()
+
+  // Collect entries whose provider/model is a prefix of the resolved model,
+  // together with the length of the matching prefix (longest match wins).
+  const matches: { entry: FallbackEntry; matchLen: number }[] = []
+  for (const entry of chain) {
+    for (const p of entry.providers) {
+      const candidate = `${p}/${entry.model}`.toLowerCase()
+      if (resolved.startsWith(candidate)) {
+        matches.push({ entry, matchLen: candidate.length })
+        break // one match per entry is enough
+      }
+    }
+  }
+
+  if (matches.length === 0) return undefined
+  matches.sort((a, b) => b.matchLen - a.matchLen)
+  return matches[0]!.entry
+}
+
+export function buildFallbackChainFromModels(
+  fallbackModels: string | (string | FallbackModelObject)[] | undefined,
+  contextProviderID: string | undefined,
+  defaultProviderID = "opencode",
+): FallbackEntry[] | undefined {
+  const normalized = normalizeFallbackModels(fallbackModels)
+  if (!normalized || normalized.length === 0) return undefined
+
+  const parsed = normalized
+    .map((entry) => {
+      if (typeof entry === "string") {
+        return parseFallbackModelEntry(entry, contextProviderID, defaultProviderID)
+      }
+      return parseFallbackModelObjectEntry(entry, contextProviderID, defaultProviderID)
+    })
+    .filter((entry): entry is FallbackEntry => entry !== undefined)
+
+  if (parsed.length === 0) return undefined
+  return parsed
+}