diff --git a/bun.lock b/bun.lock
index 798170796..04be30353 100644
--- a/bun.lock
+++ b/bun.lock
@@ -108,6 +108,14 @@
         "@oh-my-opencode/utils": "workspace:*",
       },
     },
+    "packages/prompts-core": {
+      "name": "@oh-my-opencode/prompts-core",
+      "version": "0.1.0",
+      "peerDependencies": {
+        "@oh-my-opencode/model-core": "workspace:*",
+        "@oh-my-opencode/utils": "workspace:*",
+      },
+    },
     "packages/rules-engine": {
       "name": "@oh-my-opencode/rules-engine",
       "version": "0.1.0",
@@ -209,6 +217,8 @@
 
     "@oh-my-opencode/model-core": ["@oh-my-opencode/model-core@workspace:packages/model-core"],
 
+    "@oh-my-opencode/prompts-core": ["@oh-my-opencode/prompts-core@workspace:packages/prompts-core"],
+
     "@oh-my-opencode/rules-engine": ["@oh-my-opencode/rules-engine@workspace:packages/rules-engine"],
 
     "@oh-my-opencode/utils": ["@oh-my-opencode/utils@workspace:packages/utils"],
diff --git a/package.json b/package.json
index 873783204..7a84c1328 100644
--- a/package.json
+++ b/package.json
@@ -11,6 +11,7 @@
     "packages/ast-grep-mcp",
     "packages/utils",
     "packages/model-core",
+    "packages/prompts-core",
     "packages/comment-checker-core",
     "packages/hashline-core",
     "packages/boulder-state",
@@ -49,7 +50,7 @@
     "prepublishOnly": "bun run clean && bun run build:lsp-tools-mcp && bun run build",
     "test:model-capabilities": "bun test src/shared/model-capability-aliases.test.ts src/shared/model-capability-guardrails.test.ts src/shared/model-capabilities.test.ts src/cli/doctor/checks/model-resolution.test.ts --bail",
     "typecheck": "tsgo --noEmit && bun run typecheck:packages",
-    "typecheck:packages": "tsgo --noEmit -p packages/rules-engine/tsconfig.json && tsgo --noEmit -p packages/ast-grep-core/tsconfig.json && tsgo --noEmit -p packages/ast-grep-mcp/tsconfig.json && tsgo --noEmit -p packages/utils/tsconfig.json && tsgo --noEmit -p packages/model-core/tsconfig.json && tsgo --noEmit -p packages/comment-checker-core/tsconfig.json && tsgo --noEmit -p packages/hashline-core/tsconfig.json && tsgo --noEmit -p packages/boulder-state/tsconfig.json && tsgo --noEmit -p packages/agents-md-core/tsconfig.json",
+    "typecheck:packages": "tsgo --noEmit -p packages/rules-engine/tsconfig.json && tsgo --noEmit -p packages/ast-grep-core/tsconfig.json && tsgo --noEmit -p packages/ast-grep-mcp/tsconfig.json && tsgo --noEmit -p packages/utils/tsconfig.json && tsgo --noEmit -p packages/model-core/tsconfig.json && tsgo --noEmit -p packages/prompts-core/tsconfig.json && tsgo --noEmit -p packages/comment-checker-core/tsconfig.json && tsgo --noEmit -p packages/hashline-core/tsconfig.json && tsgo --noEmit -p packages/boulder-state/tsconfig.json && tsgo --noEmit -p packages/agents-md-core/tsconfig.json",
     "typecheck:script": "tsgo --noEmit -p script/tsconfig.json",
     "test": "bun test",
     "build:ast-grep-mcp": "bun run --cwd packages/ast-grep-mcp build"
diff --git a/packages/model-core/src/index.ts b/packages/model-core/src/index.ts
index 79cb65929..a7d3c9536 100644
--- a/packages/model-core/src/index.ts
+++ b/packages/model-core/src/index.ts
@@ -1,4 +1,5 @@
 export * from "./model-requirements"
+export * from "./model-family-detectors"
 export * from "./model-capability-aliases"
 export * from "./model-capability-heuristics"
 export * from "./model-capability-guardrails"
diff --git a/packages/model-core/src/model-family-detectors.test.ts b/packages/model-core/src/model-family-detectors.test.ts
new file mode 100644
index 000000000..504e646e6
--- /dev/null
+++ b/packages/model-core/src/model-family-detectors.test.ts
@@ -0,0 +1,50 @@
+import { describe, expect, test } from "bun:test"
+import {
+  isClaudeOpus47Model,
+  isGeminiModel,
+  isGlmModel,
+  isGptModel,
+  isKimiK2Model,
+  isMiniMaxModel,
+} from "./model-family-detectors"
+
+describe("model family detectors", () => {
+  test("#given GPT model ids #then detects GPT family only", () => {
+    expect(isGptModel("openai/gpt-5.5")).toBe(true)
+    expect(isGptModel("github-copilot/gpt-4o")).toBe(true)
+    expect(isGptModel("openai/o3-mini")).toBe(false)
+    expect(isGptModel("anthropic/claude-opus-4-7")).toBe(false)
+  })
+
+  test("#given Gemini model ids #then detects Gemini family only", () => {
+    expect(isGeminiModel("google/gemini-3.1-pro")).toBe(true)
+    expect(isGeminiModel("google-vertex/gemini-3-flash")).toBe(true)
+    expect(isGeminiModel("github-copilot/gemini-3.1-pro")).toBe(true)
+    expect(isGeminiModel("openai/gpt-5.5")).toBe(false)
+  })
+
+  test("#given Kimi K2 model ids #then detects Kimi K2 family only", () => {
+    expect(isKimiK2Model("moonshotai/kimi-k2.6")).toBe(true)
+    expect(isKimiK2Model("opencode/k2p5")).toBe(true)
+    expect(isKimiK2Model("opencode/k2-p6")).toBe(true)
+    expect(isKimiK2Model("anthropic/claude-opus-4-7")).toBe(false)
+  })
+
+  test("#given GLM model ids #then detects GLM family only", () => {
+    expect(isGlmModel("z-ai/glm-5.1")).toBe(true)
+    expect(isGlmModel("opencode/glm-4.6v")).toBe(true)
+    expect(isGlmModel("google/gemini-3.1-pro")).toBe(false)
+  })
+
+  test("#given Claude Opus 4.7 model ids #then detects Opus 4.7 only", () => {
+    expect(isClaudeOpus47Model("anthropic/claude-opus-4-7")).toBe(true)
+    expect(isClaudeOpus47Model("anthropic/claude-opus-4.7")).toBe(true)
+    expect(isClaudeOpus47Model("anthropic/claude-sonnet-4-6")).toBe(false)
+  })
+
+  test("#given MiniMax model ids #then detects MiniMax family only", () => {
+    expect(isMiniMaxModel("opencode/minimax-m2.7")).toBe(true)
+    expect(isMiniMaxModel("minimax-m2.7-highspeed")).toBe(true)
+    expect(isMiniMaxModel("moonshotai/kimi-k2.6")).toBe(false)
+  })
+})
diff --git a/packages/model-core/src/model-family-detectors.ts b/packages/model-core/src/model-family-detectors.ts
new file mode 100644
index 000000000..c87203d58
--- /dev/null
+++ b/packages/model-core/src/model-family-detectors.ts
@@ -0,0 +1,45 @@
+function extractModelName(model: string): string {
+  return model.includes("/") ? (model.split("/").pop() ?? model) : model
+}
+
+export function isGptModel(model: string): boolean {
+  const modelName = extractModelName(model).toLowerCase()
+  return modelName.includes("gpt")
+}
+
+export function isClaudeOpus47Model(model: string): boolean {
+  const modelName = extractModelName(model).toLowerCase().replaceAll(".", "-")
+  return modelName.includes("claude-opus-4-7")
+}
+
+export function isKimiK2Model(model: string): boolean {
+  const modelName = extractModelName(model).toLowerCase()
+  if (modelName.includes("kimi")) return true
+  if (/k2[-.]?p[56]/.test(modelName)) return true
+  return false
+}
+
+export function isMiniMaxModel(model: string): boolean {
+  const modelName = extractModelName(model).toLowerCase()
+  return modelName.includes("minimax")
+}
+
+export function isGlmModel(model: string): boolean {
+  const modelName = extractModelName(model).toLowerCase()
+  return modelName.includes("glm")
+}
+
+const GEMINI_PROVIDERS = ["google/", "google-vertex/"] as const
+
+export function isGeminiModel(model: string): boolean {
+  if (GEMINI_PROVIDERS.some((prefix) => model.startsWith(prefix))) return true
+
+  if (
+    model.startsWith("github-copilot/") &&
+    extractModelName(model).toLowerCase().startsWith("gemini")
+  )
+    return true
+
+  const modelName = extractModelName(model).toLowerCase()
+  return modelName.startsWith("gemini-")
+}
diff --git a/packages/prompts-core/package.json b/packages/prompts-core/package.json
new file mode 100644
index 000000000..73c10187e
--- /dev/null
+++ b/packages/prompts-core/package.json
@@ -0,0 +1,22 @@
+{
+  "name": "@oh-my-opencode/prompts-core",
+  "version": "0.1.0",
+  "type": "module",
+  "private": true,
+  "description": "Harness-agnostic markdown prompt loading and model-variant routing for oh-my-opencode.",
+  "exports": {
+    ".": {
+      "types": "./index.d.ts",
+      "import": "./src/index.ts"
+    }
+  },
+  "types": "./index.d.ts",
+  "scripts": {
+    "typecheck": "tsgo --noEmit -p tsconfig.json",
+    "test": "bun test src/*.test.ts test/*.test.ts"
+  },
+  "peerDependencies": {
+    "@oh-my-opencode/model-core": "workspace:*",
+    "@oh-my-opencode/utils": "workspace:*"
+  }
+}
diff --git a/packages/prompts-core/src/__test_fixtures__/test-prompt/default.md b/packages/prompts-core/src/__test_fixtures__/test-prompt/default.md
new file mode 100644
index 000000000..4e4b14a3e
--- /dev/null
+++ b/packages/prompts-core/src/__test_fixtures__/test-prompt/default.md
@@ -0,0 +1,6 @@
+---
+title: Test Prompt
+enabled: true
+---
+Default prompt body with {X}.
+Second line remains verbatim.
diff --git a/packages/prompts-core/src/__test_fixtures__/test-prompt/gpt.md b/packages/prompts-core/src/__test_fixtures__/test-prompt/gpt.md
new file mode 100644
index 000000000..ff3925c5c
--- /dev/null
+++ b/packages/prompts-core/src/__test_fixtures__/test-prompt/gpt.md
@@ -0,0 +1,3 @@
+---
+---
+GPT prompt body with {A} and {B}.
diff --git a/packages/prompts-core/src/index.ts b/packages/prompts-core/src/index.ts
new file mode 100644
index 000000000..639fa86a7
--- /dev/null
+++ b/packages/prompts-core/src/index.ts
@@ -0,0 +1,11 @@
+export type {
+  LoadedPrompt,
+  LoadPromptInput,
+  ModelVariant,
+  PromptSource,
+  RuntimeInjection,
+  VariantTable,
+} from "./types"
+export { resolveVariant } from "./variant-resolver"
+export type { ResolveVariantInput } from "./variant-resolver"
+export { loadPrompt, PromptFileNotFoundError, PromptPathTraversalError } from "./loader"
diff --git a/packages/prompts-core/src/loader.test.ts b/packages/prompts-core/src/loader.test.ts
new file mode 100644
index 000000000..2842ab640
--- /dev/null
+++ b/packages/prompts-core/src/loader.test.ts
@@ -0,0 +1,128 @@
+import { describe, expect, test } from "bun:test"
+import { dirname, join } from "node:path"
+import { fileURLToPath } from "node:url"
+import { loadPrompt, PromptFileNotFoundError, PromptPathTraversalError } from "./loader"
+import type { PromptSource } from "./types"
+
+const fixtureSource: PromptSource = {
+  baseDir: join(dirname(fileURLToPath(import.meta.url)), "__test_fixtures__"),
+}
+
+class ResolverFailureError extends Error {
+  readonly name = "ResolverFailureError"
+}
+
+class ExpectedErrorMissingError extends Error {
+  readonly name = "ExpectedErrorMissingError"
+}
+
+describe("loadPrompt", () => {
+  test("#given markdown fixture #then returns markdown body verbatim", async () => {
+    const prompt = await loadPrompt({ source: fixtureSource, name: "test-prompt", variant: "default" })
+
+    expect(prompt.body).toBe("Default prompt body with {X}.\nSecond line remains verbatim.\n")
+  })
+
+  test("#given frontmatter fixture #then returns parsed frontmatter", async () => {
+    const prompt = await loadPrompt<{ readonly title: string; readonly enabled: boolean }>({
+      source: fixtureSource,
+      name: "test-prompt",
+      variant: "default",
+    })
+
+    expect(prompt.frontmatter.title).toBe("Test Prompt")
+    expect(prompt.frontmatter.enabled).toBe(true)
+  })
+
+  test("#given empty frontmatter #then parses without crashing", async () => {
+    const prompt = await loadPrompt({ source: fixtureSource, name: "test-prompt", variant: "gpt" })
+
+    expect(prompt.frontmatter).toEqual({})
+    expect(prompt.body).toBe("GPT prompt body with {A} and {B}.\n")
+  })
+
+  test("#given missing file #then error mentions prompt name and variant", async () => {
+    const error = await captureError(() =>
+      loadPrompt({ source: fixtureSource, name: "test-prompt", variant: "missing" })
+    )
+
+    expect(error).toBeInstanceOf(PromptFileNotFoundError)
+    expect(expectError(error).message).toContain("test-prompt/missing")
+  })
+
+  test("#given prompt name escapes source directory #then rejects path traversal", async () => {
+    const error = await captureError(() =>
+      loadPrompt({ source: fixtureSource, name: "../test-prompt", variant: "default" })
+    )
+
+    expect(error).toBeInstanceOf(PromptPathTraversalError)
+  })
+
+  test("#given variant escapes source directory #then rejects path traversal", async () => {
+    const error = await captureError(() =>
+      loadPrompt({ source: fixtureSource, name: "test-prompt", variant: "../../outside" })
+    )
+
+    expect(error).toBeInstanceOf(PromptPathTraversalError)
+  })
+
+  test("#given runtime injection #then replaces placeholder in body", async () => {
+    const prompt = await loadPrompt({
+      source: fixtureSource,
+      name: "test-prompt",
+      variant: "default",
+      inject: [{ placeholder: "{X}", resolver: () => "Y" }],
+    })
+
+    expect(prompt.body).toBe("Default prompt body with Y.\nSecond line remains verbatim.\n")
+  })
+
+  test("#given multiple runtime injections #then applies all and ignores absent placeholders", async () => {
+    const prompt = await loadPrompt({
+      source: fixtureSource,
+      name: "test-prompt",
+      variant: "gpt",
+      inject: [
+        { placeholder: "{A}", resolver: () => "Alpha" },
+        { placeholder: "{B}", resolver: () => "Beta" },
+        { placeholder: "{ABSENT}", resolver: () => "No-op" },
+      ],
+    })
+
+    expect(prompt.body).toBe("GPT prompt body with Alpha and Beta.\n")
+  })
+
+  test("#given injection resolver throws #then propagates the error", async () => {
+    const error = await captureError(() =>
+      loadPrompt({
+        source: fixtureSource,
+        name: "test-prompt",
+        variant: "default",
+        inject: [
+          {
+            placeholder: "{X}",
+            resolver: () => {
+              throw new ResolverFailureError("resolver failed")
+            },
+          },
+        ],
+      })
+    )
+
+    expect(error).toBeInstanceOf(ResolverFailureError)
+  })
+})
+
+async function captureError(operation: () => Promise<unknown>): Promise<unknown> {
+  try {
+    await operation()
+    return undefined
+  } catch (error) {
+    return error
+  }
+}
+
+function expectError(error: unknown): Error {
+  if (error instanceof Error) return error
+  throw new ExpectedErrorMissingError("Expected operation to throw an Error instance")
+}
diff --git a/packages/prompts-core/src/loader.ts b/packages/prompts-core/src/loader.ts
new file mode 100644
index 000000000..df01b4579
--- /dev/null
+++ b/packages/prompts-core/src/loader.ts
@@ -0,0 +1,82 @@
+import { parseFrontmatter } from "@oh-my-opencode/utils"
+import { readFile } from "node:fs/promises"
+import { isAbsolute, relative, resolve } from "node:path"
+import type { LoadedPrompt, LoadPromptInput, RuntimeInjection } from "./types"
+
+export class PromptFileNotFoundError extends Error {
+  readonly name = "PromptFileNotFoundError"
+
+  constructor(
+    readonly promptName: string,
+    readonly variant: string,
+    readonly filePath: string,
+    options?: ErrorOptions
+  ) {
+    super(`Prompt file not found for ${promptName}/${variant}: ${filePath}`, options)
+  }
+}
+
+export class PromptPathTraversalError extends Error {
+  readonly name = "PromptPathTraversalError"
+
+  constructor(
+    readonly promptName: string,
+    readonly variant: string
+  ) {
+    super(`Prompt path escapes source directory for ${promptName}/${variant}`)
+  }
+}
+
+export async function loadPrompt<TFrontmatter = Record<string, unknown>>(
+  input: LoadPromptInput
+): Promise<LoadedPrompt<TFrontmatter>> {
+  const filePath = resolvePromptFilePath(input.source.baseDir, input.name, input.variant)
+  const content = await readPromptFile(input.name, input.variant, filePath)
+  const parsed = parseFrontmatter<TFrontmatter>(content)
+  const body = await applyRuntimeInjections(parsed.body, input.inject ?? [])
+
+  return {
+    frontmatter: parsed.data,
+    body,
+    hadFrontmatter: parsed.hadFrontmatter,
+    parseError: parsed.parseError,
+    filePath,
+  }
+}
+
+function resolvePromptFilePath(baseDir: string, promptName: string, variant: string): string {
+  const resolvedBaseDir = resolve(baseDir)
+  const filePath = resolve(resolvedBaseDir, promptName, `${variant}.md`)
+  const relativePath = relative(resolvedBaseDir, filePath)
+  if (relativePath.startsWith("..") || isAbsolute(relativePath)) {
+    throw new PromptPathTraversalError(promptName, variant)
+  }
+  return filePath
+}
+
+async function readPromptFile(promptName: string, variant: string, filePath: string): Promise<string> {
+  try {
+    return await readFile(filePath, "utf8")
+  } catch (error) {
+    if (error instanceof Error && getErrorCode(error) === "ENOENT") {
+      throw new PromptFileNotFoundError(promptName, variant, filePath, { cause: error })
+    }
+    throw error
+  }
+}
+
+async function applyRuntimeInjections(
+  body: string,
+  injections: readonly RuntimeInjection[]
+): Promise<string> {
+  let renderedBody = body
+  for (const injection of injections) {
+    renderedBody = renderedBody.replaceAll(injection.placeholder, await injection.resolver())
+  }
+  return renderedBody
+}
+
+function getErrorCode(error: Error): string | undefined {
+  if (!("code" in error)) return undefined
+  return typeof error.code === "string" ? error.code : undefined
+}
diff --git a/packages/prompts-core/src/types.test.ts b/packages/prompts-core/src/types.test.ts
new file mode 100644
index 000000000..50b1a4b47
--- /dev/null
+++ b/packages/prompts-core/src/types.test.ts
@@ -0,0 +1,32 @@
+import { describe, expect, test } from "bun:test"
+import type { LoadPromptInput, LoadedPrompt, PromptSource, RuntimeInjection } from "./types"
+
+describe("prompt core types", () => {
+  test("#given loader input shape #then accepts source name variant and runtime injections", () => {
+    const source: PromptSource = { baseDir: "/tmp/prompts" }
+    const injection: RuntimeInjection = { placeholder: "{X}", resolver: () => "Y" }
+
+    const input = {
+      source,
+      name: "test",
+      variant: "default",
+      inject: [injection],
+    } satisfies LoadPromptInput
+
+    expect(input.source.baseDir).toBe("/tmp/prompts")
+    expect(input.inject[0]?.placeholder).toBe("{X}")
+  })
+
+  test("#given loaded prompt shape #then carries frontmatter and rendered body", () => {
+    const loaded = {
+      frontmatter: { title: "Fixture" },
+      body: "Prompt body",
+      hadFrontmatter: true,
+      parseError: false,
+      filePath: "/tmp/prompts/test/default.md",
+    } satisfies LoadedPrompt<{ readonly title: string }>
+
+    expect(loaded.frontmatter.title).toBe("Fixture")
+    expect(loaded.body).toBe("Prompt body")
+  })
+})
diff --git a/packages/prompts-core/src/types.ts b/packages/prompts-core/src/types.ts
new file mode 100644
index 000000000..c70351455
--- /dev/null
+++ b/packages/prompts-core/src/types.ts
@@ -0,0 +1,35 @@
+export type ModelVariant =
+  | "default"
+  | "gpt"
+  | "gemini"
+  | "kimi"
+  | "glm"
+  | "planner"
+  | "opus-4-7"
+  | "minimax"
+
+export type PromptSource = {
+  readonly baseDir: string
+}
+
+export type RuntimeInjection = {
+  readonly placeholder: string
+  readonly resolver: () => string | Promise<string>
+}
+
+export type LoadPromptInput = {
+  readonly source: PromptSource
+  readonly name: string
+  readonly variant: string
+  readonly inject?: readonly RuntimeInjection[]
+}
+
+export type LoadedPrompt<TFrontmatter = Record<string, unknown>> = {
+  readonly frontmatter: TFrontmatter
+  readonly body: string
+  readonly hadFrontmatter: boolean
+  readonly parseError: boolean
+  readonly filePath: string
+}
+
+export type VariantTable = Readonly<Record<string, PromptSource>>
diff --git a/packages/prompts-core/src/variant-resolver.test.ts b/packages/prompts-core/src/variant-resolver.test.ts
new file mode 100644
index 000000000..303e3d028
--- /dev/null
+++ b/packages/prompts-core/src/variant-resolver.test.ts
@@ -0,0 +1,50 @@
+import { describe, expect, test } from "bun:test"
+import type { PromptSource, VariantTable } from "./types"
+import { resolveVariant } from "./variant-resolver"
+
+const promptSource = (baseDir: string): PromptSource => ({ baseDir })
+
+const variants = {
+  planner: promptSource("/prompts/planner"),
+  gpt: promptSource("/prompts/gpt"),
+  gemini: promptSource("/prompts/gemini"),
+  kimi: promptSource("/prompts/kimi"),
+  glm: promptSource("/prompts/glm"),
+  default: promptSource("/prompts/default"),
+} satisfies VariantTable
+
+describe("resolveVariant", () => {
+  test("#given Claude Opus 4.7 model #then resolves default variant", () => {
+    expect(resolveVariant({ modelID: "claude-opus-4-7", variants })).toBe("default")
+  })
+
+  test("#given GPT model #then resolves gpt variant", () => {
+    expect(resolveVariant({ modelID: "gpt-5-5", variants })).toBe("gpt")
+  })
+
+  test("#given Gemini model #then resolves gemini variant", () => {
+    expect(resolveVariant({ modelID: "gemini-3-1-pro", variants })).toBe("gemini")
+  })
+
+  test("#given Kimi K2 model #then resolves kimi variant", () => {
+    expect(resolveVariant({ modelID: "kimi-k2-6", variants })).toBe("kimi")
+  })
+
+  test("#given GLM model #then resolves glm variant", () => {
+    expect(resolveVariant({ modelID: "glm-5-1", variants })).toBe("glm")
+  })
+
+  test("#given Prometheus agent #then planner overrides model variant", () => {
+    expect(resolveVariant({ agentName: "prometheus", modelID: "gpt-5-5", variants })).toBe(
+      "planner"
+    )
+  })
+
+  test("#given unknown model #then falls back to default variant", () => {
+    expect(resolveVariant({ modelID: "claude-haiku-4-5", variants })).toBe("default")
+  })
+
+  test("#given empty variants table #then throws TypeError", () => {
+    expect(() => resolveVariant({ modelID: "gpt-5-5", variants: {} })).toThrow(TypeError)
+  })
+})
diff --git a/packages/prompts-core/src/variant-resolver.ts b/packages/prompts-core/src/variant-resolver.ts
new file mode 100644
index 000000000..605924c5f
--- /dev/null
+++ b/packages/prompts-core/src/variant-resolver.ts
@@ -0,0 +1,58 @@
+import {
+  isClaudeOpus47Model,
+  isGeminiModel,
+  isGlmModel,
+  isGptModel,
+  isKimiK2Model,
+  isMiniMaxModel,
+} from "@oh-my-opencode/model-core"
+import type { VariantTable } from "./types"
+
+type ModelMatcher = (modelID: string) => boolean
+
+export type ResolveVariantInput = {
+  readonly modelID?: string
+  readonly agentName?: string
+  readonly variants: VariantTable
+}
+
+const PLANNER_AGENT_NAMES: ReadonlySet<string> = new Set(["prometheus"] as const)
+
+const MODEL_MATCHERS: Readonly<Record<string, ModelMatcher>> = {
+  gpt: isGptModel,
+  gemini: isGeminiModel,
+  kimi: isKimiK2Model,
+  glm: isGlmModel,
+  "opus-4-7": isClaudeOpus47Model,
+  minimax: isMiniMaxModel,
+}
+
+export function resolveVariant(input: ResolveVariantInput): string {
+  const variantNames = Object.keys(input.variants)
+  if (variantNames.length === 0) {
+    throw new TypeError("resolveVariant requires at least one prompt variant")
+  }
+
+  if (isPlannerAgent(input.agentName) && variantNames.includes("planner")) {
+    return "planner"
+  }
+
+  if (input.modelID !== undefined) {
+    for (const variantName of variantNames) {
+      if (matchesModelVariant(variantName, input.modelID)) return variantName
+    }
+  }
+
+  if (variantNames.includes("default")) return "default"
+
+  return variantNames[0]
+}
+
+function isPlannerAgent(agentName: string | undefined): boolean {
+  return agentName !== undefined && PLANNER_AGENT_NAMES.has(agentName.toLowerCase())
+}
+
+function matchesModelVariant(variantName: string, modelID: string): boolean {
+  const matcher = MODEL_MATCHERS[variantName]
+  return matcher?.(modelID) ?? false
+}
diff --git a/packages/prompts-core/test/opencode-coupling-audit.test.ts b/packages/prompts-core/test/opencode-coupling-audit.test.ts
new file mode 100644
index 000000000..4205fdc92
--- /dev/null
+++ b/packages/prompts-core/test/opencode-coupling-audit.test.ts
@@ -0,0 +1,42 @@
+import { describe, expect, test } from "bun:test"
+import { readdir, readFile } from "node:fs/promises"
+import { dirname, join } from "node:path"
+import { fileURLToPath } from "node:url"
+
+const SOURCE_DIR = join(dirname(fileURLToPath(import.meta.url)), "../src")
+
+describe("opencode coupling audit", () => {
+  test("#given prompts-core source #then no file imports @opencode-ai packages", async () => {
+    const offenders = await findOpenCodeImports(SOURCE_DIR)
+
+    expect(offenders).toEqual([])
+  })
+})
+
+async function findOpenCodeImports(sourceDir: string): Promise<readonly string[]> {
+  const files = await collectTypeScriptFiles(sourceDir)
+  const offenders: string[] = []
+
+  for (const filePath of files) {
+    const source = await readFile(filePath, "utf8")
+    if (source.includes("@opencode-ai")) offenders.push(filePath)
+  }
+
+  return offenders
+}
+
+async function collectTypeScriptFiles(directory: string): Promise<readonly string[]> {
+  const entries = await readdir(directory, { withFileTypes: true })
+  const files: string[] = []
+
+  for (const entry of entries) {
+    const entryPath = join(directory, entry.name)
+    if (entry.isDirectory()) {
+      files.push(...(await collectTypeScriptFiles(entryPath)))
+    } else if (entry.isFile() && entry.name.endsWith(".ts")) {
+      files.push(entryPath)
+    }
+  }
+
+  return files
+}
diff --git a/packages/prompts-core/tsconfig.json b/packages/prompts-core/tsconfig.json
new file mode 100644
index 000000000..6a768d440
--- /dev/null
+++ b/packages/prompts-core/tsconfig.json
@@ -0,0 +1,14 @@
+{
+  "compilerOptions": {
+    "target": "ESNext",
+    "module": "ESNext",
+    "moduleResolution": "bundler",
+    "strict": true,
+    "esModuleInterop": true,
+    "skipLibCheck": true,
+    "forceConsistentCasingInFileNames": true,
+    "lib": ["ESNext"],
+    "types": ["bun-types"]
+  },
+  "include": ["src/**/*", "test/**/*"]
+}
diff --git a/src/agents/types.ts b/src/agents/types.ts
index 111cdefc0..9b582527f 100644
--- a/src/agents/types.ts
+++ b/src/agents/types.ts
@@ -1,5 +1,14 @@
 import type { AgentConfig } from "@opencode-ai/sdk";
 
+export {
+  isClaudeOpus47Model,
+  isGeminiModel,
+  isGlmModel,
+  isGptModel,
+  isKimiK2Model,
+  isMiniMaxModel,
+} from "@oh-my-opencode/model-core";
+
 /**
  * Agent mode determines UI model selection behavior:
  * - "primary": Respects user's UI-selected model (sisyphus, atlas)
@@ -74,11 +83,6 @@ function extractModelName(model: string): string {
   return model.includes("/") ? (model.split("/").pop() ?? model) : model;
 }
 
-export function isGptModel(model: string): boolean {
-  const modelName = extractModelName(model).toLowerCase();
-  return modelName.includes("gpt");
-}
-
 const GPT_NATIVE_SISYPHUS_RE = /gpt-5[.-](?:[4-9]|\d{2,})/i;
 
 export function isGptNativeSisyphusModel(model: string): boolean {
@@ -101,53 +105,6 @@ export function isGpt5_2Model(model: string): boolean {
   return modelName.includes("gpt-5.2") || modelName.includes("gpt-5-2");
 }
 
-export function isClaudeOpus47Model(model: string): boolean {
-  const modelName = extractModelName(model).toLowerCase().replaceAll(".", "-");
-  return modelName.includes("claude-opus-4-7");
-}
-
-/**
- * Kimi K2.x model detection (K2.5 / K2.6 family).
- *
- * Matches model IDs containing any of:
- *   - "kimi" (provider/family signal — kimi-k2.6, moonshotai/Kimi-K2.6, etc.)
- *   - "k2p5" / "k2-p5" / "k2.p5"
- *   - "k2p6" / "k2-p6" / "k2.p6"
- *
- * Match is case-insensitive on the model name (last path segment).
- */
-export function isKimiK2Model(model: string): boolean {
-  const modelName = extractModelName(model).toLowerCase();
-  if (modelName.includes("kimi")) return true;
-  if (/k2[-.]?p[56]/.test(modelName)) return true;
-  return false;
-}
-
-const GEMINI_PROVIDERS = ["google/", "google-vertex/"];
-
-export function isMiniMaxModel(model: string): boolean {
-  const modelName = extractModelName(model).toLowerCase();
-  return modelName.includes("minimax");
-}
-
-export function isGlmModel(model: string): boolean {
-  const modelName = extractModelName(model).toLowerCase();
-  return modelName.includes("glm");
-}
-
-export function isGeminiModel(model: string): boolean {
-  if (GEMINI_PROVIDERS.some((prefix) => model.startsWith(prefix))) return true;
-
-  if (
-    model.startsWith("github-copilot/") &&
-    extractModelName(model).toLowerCase().startsWith("gemini")
-  )
-    return true;
-
-  const modelName = extractModelName(model).toLowerCase();
-  return modelName.startsWith("gemini-");
-}
-
 export type BuiltinAgentName =
   | "sisyphus"
   | "hephaestus"