diff --git a/.omo/evidence/pr1-prompts-core/s1.red.log b/.omo/evidence/pr1-prompts-core/s1.red.log
new file mode 100644
index 000000000..e6577d62b
--- /dev/null
+++ b/.omo/evidence/pr1-prompts-core/s1.red.log
@@ -0,0 +1,113 @@
+bun test v1.3.12 (700fc117)
+
+packages/prompts-core/src/variant-resolver.test.ts:
+S1 actual: __red__
+27 |       // when
+28 |       const actual = resolveVariant({ modelID: "claude-opus-4-7", variants })
+29 | 
+30 |       // then
+31 |       console.info("S1 actual:", actual)
+32 |       expect(actual).toBe("default")
+                          ^
+error: expect(received).toBe(expected)
+
+Expected: "default"
+Received: "__red__"
+
+      at <anonymous> (/Users/yeongyu/local-workspaces/omo-wt/feat/prompts-core-foundation/packages/prompts-core/src/variant-resolver.test.ts:32:22)
+(fail) resolveVariant > #given declared model variants > #when claude opus has no model match #then returns default fallback [0.39ms]
+S2 actual: __red__
+43 |       // when
+44 |       const actual = resolveVariant({ modelID: "openai/gpt-5.5", variants })
+45 | 
+46 |       // then
+47 |       console.info("S2 actual:", actual)
+48 |       expect(actual).toBe("gpt")
+                          ^
+error: expect(received).toBe(expected)
+
+Expected: "gpt"
+Received: "__red__"
+
+      at <anonymous> (/Users/yeongyu/local-workspaces/omo-wt/feat/prompts-core-foundation/packages/prompts-core/src/variant-resolver.test.ts:48:22)
+(fail) resolveVariant > #given declared model variants > #when openai gpt model matches #then returns gpt [0.10ms]
+S3 actual: __red__
+59 |       // when
+60 |       const actual = resolveVariant({ modelID: "google/gemini-3-1-pro", variants })
+61 | 
+62 |       // then
+63 |       console.info("S3 actual:", actual)
+64 |       expect(actual).toBe("gemini")
+                          ^
+error: expect(received).toBe(expected)
+
+Expected: "gemini"
+Received: "__red__"
+
+      at <anonymous> (/Users/yeongyu/local-workspaces/omo-wt/feat/prompts-core-foundation/packages/prompts-core/src/variant-resolver.test.ts:64:22)
+(fail) resolveVariant > #given declared model variants > #when google gemini model matches #then returns gemini [0.04ms]
+S4 actual: __red__
+80 |         variants,
+81 |       })
+82 | 
+83 |       // then
+84 |       console.info("S4 actual:", actual)
+85 |       expect(actual).toBe("planner")
+                          ^
+error: expect(received).toBe(expected)
+
+Expected: "planner"
+Received: "__red__"
+
+      at <anonymous> (/Users/yeongyu/local-workspaces/omo-wt/feat/prompts-core-foundation/packages/prompts-core/src/variant-resolver.test.ts:85:22)
+(fail) resolveVariant > #given agent and fallback variants > #when agent and model both match #then declared agent variant wins [0.12ms]
+S5 actual: __red__
+94 |       // when
+95 |       const actual = resolveVariant({ variants })
+96 | 
+97 |       // then
+98 |       console.info("S5 actual:", actual)
+99 |       expect(actual).toBe("default")
+                          ^
+error: expect(received).toBe(expected)
+
+Expected: "default"
+Received: "__red__"
+
+      at <anonymous> (/Users/yeongyu/local-workspaces/omo-wt/feat/prompts-core-foundation/packages/prompts-core/src/variant-resolver.test.ts:99:22)
+(fail) resolveVariant > #given agent and fallback variants > #when no context is provided #then returns default fallback [0.08ms]
+S6 actual: __red__
+109 |       // when
+110 |       const actual = resolveVariant({ modelID: "unknown-model", variants })
+111 | 
+112 |       // then
+113 |       console.info("S6 actual:", actual)
+114 |       expect(actual).toBe("default")
+                           ^
+error: expect(received).toBe(expected)
+
+Expected: "default"
+Received: "__red__"
+
+      at <anonymous> (/Users/yeongyu/local-workspaces/omo-wt/feat/prompts-core-foundation/packages/prompts-core/src/variant-resolver.test.ts:114:22)
+(fail) resolveVariant > #given agent and fallback variants > #when no variant test matches #then returns fallback [0.07ms]
+S7 actual: __red__
+134 |         }
+135 |       }
+136 |       console.info("S7 actual:", actual)
+137 | 
+138 |       // then
+139 |       expect(thrown).toBeInstanceOf(NoMatchingVariantError)
+                           ^
+error: expect(received).toBeInstanceOf(expected)
+
+Expected constructor: [class NoMatchingVariantError extends Error]
+Received value: undefined
+
+      at <anonymous> (/Users/yeongyu/local-workspaces/omo-wt/feat/prompts-core-foundation/packages/prompts-core/src/variant-resolver.test.ts:139:22)
+(fail) resolveVariant > #given agent and fallback variants > #when no variant matches and no fallback exists #then throws [0.09ms]
+
+ 0 pass
+ 7 fail
+ 7 expect() calls
+Ran 7 tests across 1 file. [74.00ms]
diff --git a/.omo/evidence/pr1-prompts-core/s2.red.log b/.omo/evidence/pr1-prompts-core/s2.red.log
new file mode 100644
index 000000000..e6577d62b
--- /dev/null
+++ b/.omo/evidence/pr1-prompts-core/s2.red.log
@@ -0,0 +1,113 @@
+bun test v1.3.12 (700fc117)
+
+packages/prompts-core/src/variant-resolver.test.ts:
+S1 actual: __red__
+27 |       // when
+28 |       const actual = resolveVariant({ modelID: "claude-opus-4-7", variants })
+29 | 
+30 |       // then
+31 |       console.info("S1 actual:", actual)
+32 |       expect(actual).toBe("default")
+                          ^
+error: expect(received).toBe(expected)
+
+Expected: "default"
+Received: "__red__"
+
+      at <anonymous> (/Users/yeongyu/local-workspaces/omo-wt/feat/prompts-core-foundation/packages/prompts-core/src/variant-resolver.test.ts:32:22)
+(fail) resolveVariant > #given declared model variants > #when claude opus has no model match #then returns default fallback [0.39ms]
+S2 actual: __red__
+43 |       // when
+44 |       const actual = resolveVariant({ modelID: "openai/gpt-5.5", variants })
+45 | 
+46 |       // then
+47 |       console.info("S2 actual:", actual)
+48 |       expect(actual).toBe("gpt")
+                          ^
+error: expect(received).toBe(expected)
+
+Expected: "gpt"
+Received: "__red__"
+
+      at <anonymous> (/Users/yeongyu/local-workspaces/omo-wt/feat/prompts-core-foundation/packages/prompts-core/src/variant-resolver.test.ts:48:22)
+(fail) resolveVariant > #given declared model variants > #when openai gpt model matches #then returns gpt [0.10ms]
+S3 actual: __red__
+59 |       // when
+60 |       const actual = resolveVariant({ modelID: "google/gemini-3-1-pro", variants })
+61 | 
+62 |       // then
+63 |       console.info("S3 actual:", actual)
+64 |       expect(actual).toBe("gemini")
+                          ^
+error: expect(received).toBe(expected)
+
+Expected: "gemini"
+Received: "__red__"
+
+      at <anonymous> (/Users/yeongyu/local-workspaces/omo-wt/feat/prompts-core-foundation/packages/prompts-core/src/variant-resolver.test.ts:64:22)
+(fail) resolveVariant > #given declared model variants > #when google gemini model matches #then returns gemini [0.04ms]
+S4 actual: __red__
+80 |         variants,
+81 |       })
+82 | 
+83 |       // then
+84 |       console.info("S4 actual:", actual)
+85 |       expect(actual).toBe("planner")
+                          ^
+error: expect(received).toBe(expected)
+
+Expected: "planner"
+Received: "__red__"
+
+      at <anonymous> (/Users/yeongyu/local-workspaces/omo-wt/feat/prompts-core-foundation/packages/prompts-core/src/variant-resolver.test.ts:85:22)
+(fail) resolveVariant > #given agent and fallback variants > #when agent and model both match #then declared agent variant wins [0.12ms]
+S5 actual: __red__
+94 |       // when
+95 |       const actual = resolveVariant({ variants })
+96 | 
+97 |       // then
+98 |       console.info("S5 actual:", actual)
+99 |       expect(actual).toBe("default")
+                          ^
+error: expect(received).toBe(expected)
+
+Expected: "default"
+Received: "__red__"
+
+      at <anonymous> (/Users/yeongyu/local-workspaces/omo-wt/feat/prompts-core-foundation/packages/prompts-core/src/variant-resolver.test.ts:99:22)
+(fail) resolveVariant > #given agent and fallback variants > #when no context is provided #then returns default fallback [0.08ms]
+S6 actual: __red__
+109 |       // when
+110 |       const actual = resolveVariant({ modelID: "unknown-model", variants })
+111 | 
+112 |       // then
+113 |       console.info("S6 actual:", actual)
+114 |       expect(actual).toBe("default")
+                           ^
+error: expect(received).toBe(expected)
+
+Expected: "default"
+Received: "__red__"
+
+      at <anonymous> (/Users/yeongyu/local-workspaces/omo-wt/feat/prompts-core-foundation/packages/prompts-core/src/variant-resolver.test.ts:114:22)
+(fail) resolveVariant > #given agent and fallback variants > #when no variant test matches #then returns fallback [0.07ms]
+S7 actual: __red__
+134 |         }
+135 |       }
+136 |       console.info("S7 actual:", actual)
+137 | 
+138 |       // then
+139 |       expect(thrown).toBeInstanceOf(NoMatchingVariantError)
+                           ^
+error: expect(received).toBeInstanceOf(expected)
+
+Expected constructor: [class NoMatchingVariantError extends Error]
+Received value: undefined
+
+      at <anonymous> (/Users/yeongyu/local-workspaces/omo-wt/feat/prompts-core-foundation/packages/prompts-core/src/variant-resolver.test.ts:139:22)
+(fail) resolveVariant > #given agent and fallback variants > #when no variant matches and no fallback exists #then throws [0.09ms]
+
+ 0 pass
+ 7 fail
+ 7 expect() calls
+Ran 7 tests across 1 file. [74.00ms]
diff --git a/.omo/evidence/pr1-prompts-core/s3.red.log b/.omo/evidence/pr1-prompts-core/s3.red.log
new file mode 100644
index 000000000..e6577d62b
--- /dev/null
+++ b/.omo/evidence/pr1-prompts-core/s3.red.log
@@ -0,0 +1,113 @@
+bun test v1.3.12 (700fc117)
+
+packages/prompts-core/src/variant-resolver.test.ts:
+S1 actual: __red__
+27 |       // when
+28 |       const actual = resolveVariant({ modelID: "claude-opus-4-7", variants })
+29 | 
+30 |       // then
+31 |       console.info("S1 actual:", actual)
+32 |       expect(actual).toBe("default")
+                          ^
+error: expect(received).toBe(expected)
+
+Expected: "default"
+Received: "__red__"
+
+      at <anonymous> (/Users/yeongyu/local-workspaces/omo-wt/feat/prompts-core-foundation/packages/prompts-core/src/variant-resolver.test.ts:32:22)
+(fail) resolveVariant > #given declared model variants > #when claude opus has no model match #then returns default fallback [0.39ms]
+S2 actual: __red__
+43 |       // when
+44 |       const actual = resolveVariant({ modelID: "openai/gpt-5.5", variants })
+45 | 
+46 |       // then
+47 |       console.info("S2 actual:", actual)
+48 |       expect(actual).toBe("gpt")
+                          ^
+error: expect(received).toBe(expected)
+
+Expected: "gpt"
+Received: "__red__"
+
+      at <anonymous> (/Users/yeongyu/local-workspaces/omo-wt/feat/prompts-core-foundation/packages/prompts-core/src/variant-resolver.test.ts:48:22)
+(fail) resolveVariant > #given declared model variants > #when openai gpt model matches #then returns gpt [0.10ms]
+S3 actual: __red__
+59 |       // when
+60 |       const actual = resolveVariant({ modelID: "google/gemini-3-1-pro", variants })
+61 | 
+62 |       // then
+63 |       console.info("S3 actual:", actual)
+64 |       expect(actual).toBe("gemini")
+                          ^
+error: expect(received).toBe(expected)
+
+Expected: "gemini"
+Received: "__red__"
+
+      at <anonymous> (/Users/yeongyu/local-workspaces/omo-wt/feat/prompts-core-foundation/packages/prompts-core/src/variant-resolver.test.ts:64:22)
+(fail) resolveVariant > #given declared model variants > #when google gemini model matches #then returns gemini [0.04ms]
+S4 actual: __red__
+80 |         variants,
+81 |       })
+82 | 
+83 |       // then
+84 |       console.info("S4 actual:", actual)
+85 |       expect(actual).toBe("planner")
+                          ^
+error: expect(received).toBe(expected)
+
+Expected: "planner"
+Received: "__red__"
+
+      at <anonymous> (/Users/yeongyu/local-workspaces/omo-wt/feat/prompts-core-foundation/packages/prompts-core/src/variant-resolver.test.ts:85:22)
+(fail) resolveVariant > #given agent and fallback variants > #when agent and model both match #then declared agent variant wins [0.12ms]
+S5 actual: __red__
+94 |       // when
+95 |       const actual = resolveVariant({ variants })
+96 | 
+97 |       // then
+98 |       console.info("S5 actual:", actual)
+99 |       expect(actual).toBe("default")
+                          ^
+error: expect(received).toBe(expected)
+
+Expected: "default"
+Received: "__red__"
+
+      at <anonymous> (/Users/yeongyu/local-workspaces/omo-wt/feat/prompts-core-foundation/packages/prompts-core/src/variant-resolver.test.ts:99:22)
+(fail) resolveVariant > #given agent and fallback variants > #when no context is provided #then returns default fallback [0.08ms]
+S6 actual: __red__
+109 |       // when
+110 |       const actual = resolveVariant({ modelID: "unknown-model", variants })
+111 | 
+112 |       // then
+113 |       console.info("S6 actual:", actual)
+114 |       expect(actual).toBe("default")
+                           ^
+error: expect(received).toBe(expected)
+
+Expected: "default"
+Received: "__red__"
+
+      at <anonymous> (/Users/yeongyu/local-workspaces/omo-wt/feat/prompts-core-foundation/packages/prompts-core/src/variant-resolver.test.ts:114:22)
+(fail) resolveVariant > #given agent and fallback variants > #when no variant test matches #then returns fallback [0.07ms]
+S7 actual: __red__
+134 |         }
+135 |       }
+136 |       console.info("S7 actual:", actual)
+137 | 
+138 |       // then
+139 |       expect(thrown).toBeInstanceOf(NoMatchingVariantError)
+                           ^
+error: expect(received).toBeInstanceOf(expected)
+
+Expected constructor: [class NoMatchingVariantError extends Error]
+Received value: undefined
+
+      at <anonymous> (/Users/yeongyu/local-workspaces/omo-wt/feat/prompts-core-foundation/packages/prompts-core/src/variant-resolver.test.ts:139:22)
+(fail) resolveVariant > #given agent and fallback variants > #when no variant matches and no fallback exists #then throws [0.09ms]
+
+ 0 pass
+ 7 fail
+ 7 expect() calls
+Ran 7 tests across 1 file. [74.00ms]
diff --git a/.omo/evidence/pr1-prompts-core/s4.red.log b/.omo/evidence/pr1-prompts-core/s4.red.log
new file mode 100644
index 000000000..e6577d62b
--- /dev/null
+++ b/.omo/evidence/pr1-prompts-core/s4.red.log
@@ -0,0 +1,113 @@
+bun test v1.3.12 (700fc117)
+
+packages/prompts-core/src/variant-resolver.test.ts:
+S1 actual: __red__
+27 |       // when
+28 |       const actual = resolveVariant({ modelID: "claude-opus-4-7", variants })
+29 | 
+30 |       // then
+31 |       console.info("S1 actual:", actual)
+32 |       expect(actual).toBe("default")
+                          ^
+error: expect(received).toBe(expected)
+
+Expected: "default"
+Received: "__red__"
+
+      at <anonymous> (/Users/yeongyu/local-workspaces/omo-wt/feat/prompts-core-foundation/packages/prompts-core/src/variant-resolver.test.ts:32:22)
+(fail) resolveVariant > #given declared model variants > #when claude opus has no model match #then returns default fallback [0.39ms]
+S2 actual: __red__
+43 |       // when
+44 |       const actual = resolveVariant({ modelID: "openai/gpt-5.5", variants })
+45 | 
+46 |       // then
+47 |       console.info("S2 actual:", actual)
+48 |       expect(actual).toBe("gpt")
+                          ^
+error: expect(received).toBe(expected)
+
+Expected: "gpt"
+Received: "__red__"
+
+      at <anonymous> (/Users/yeongyu/local-workspaces/omo-wt/feat/prompts-core-foundation/packages/prompts-core/src/variant-resolver.test.ts:48:22)
+(fail) resolveVariant > #given declared model variants > #when openai gpt model matches #then returns gpt [0.10ms]
+S3 actual: __red__
+59 |       // when
+60 |       const actual = resolveVariant({ modelID: "google/gemini-3-1-pro", variants })
+61 | 
+62 |       // then
+63 |       console.info("S3 actual:", actual)
+64 |       expect(actual).toBe("gemini")
+                          ^
+error: expect(received).toBe(expected)
+
+Expected: "gemini"
+Received: "__red__"
+
+      at <anonymous> (/Users/yeongyu/local-workspaces/omo-wt/feat/prompts-core-foundation/packages/prompts-core/src/variant-resolver.test.ts:64:22)
+(fail) resolveVariant > #given declared model variants > #when google gemini model matches #then returns gemini [0.04ms]
+S4 actual: __red__
+80 |         variants,
+81 |       })
+82 | 
+83 |       // then
+84 |       console.info("S4 actual:", actual)
+85 |       expect(actual).toBe("planner")
+                          ^
+error: expect(received).toBe(expected)
+
+Expected: "planner"
+Received: "__red__"
+
+      at <anonymous> (/Users/yeongyu/local-workspaces/omo-wt/feat/prompts-core-foundation/packages/prompts-core/src/variant-resolver.test.ts:85:22)
+(fail) resolveVariant > #given agent and fallback variants > #when agent and model both match #then declared agent variant wins [0.12ms]
+S5 actual: __red__
+94 |       // when
+95 |       const actual = resolveVariant({ variants })
+96 | 
+97 |       // then
+98 |       console.info("S5 actual:", actual)
+99 |       expect(actual).toBe("default")
+                          ^
+error: expect(received).toBe(expected)
+
+Expected: "default"
+Received: "__red__"
+
+      at <anonymous> (/Users/yeongyu/local-workspaces/omo-wt/feat/prompts-core-foundation/packages/prompts-core/src/variant-resolver.test.ts:99:22)
+(fail) resolveVariant > #given agent and fallback variants > #when no context is provided #then returns default fallback [0.08ms]
+S6 actual: __red__
+109 |       // when
+110 |       const actual = resolveVariant({ modelID: "unknown-model", variants })
+111 | 
+112 |       // then
+113 |       console.info("S6 actual:", actual)
+114 |       expect(actual).toBe("default")
+                           ^
+error: expect(received).toBe(expected)
+
+Expected: "default"
+Received: "__red__"
+
+      at <anonymous> (/Users/yeongyu/local-workspaces/omo-wt/feat/prompts-core-foundation/packages/prompts-core/src/variant-resolver.test.ts:114:22)
+(fail) resolveVariant > #given agent and fallback variants > #when no variant test matches #then returns fallback [0.07ms]
+S7 actual: __red__
+134 |         }
+135 |       }
+136 |       console.info("S7 actual:", actual)
+137 | 
+138 |       // then
+139 |       expect(thrown).toBeInstanceOf(NoMatchingVariantError)
+                           ^
+error: expect(received).toBeInstanceOf(expected)
+
+Expected constructor: [class NoMatchingVariantError extends Error]
+Received value: undefined
+
+      at <anonymous> (/Users/yeongyu/local-workspaces/omo-wt/feat/prompts-core-foundation/packages/prompts-core/src/variant-resolver.test.ts:139:22)
+(fail) resolveVariant > #given agent and fallback variants > #when no variant matches and no fallback exists #then throws [0.09ms]
+
+ 0 pass
+ 7 fail
+ 7 expect() calls
+Ran 7 tests across 1 file. [74.00ms]
diff --git a/.omo/evidence/pr1-prompts-core/s5.red.log b/.omo/evidence/pr1-prompts-core/s5.red.log
new file mode 100644
index 000000000..e6577d62b
--- /dev/null
+++ b/.omo/evidence/pr1-prompts-core/s5.red.log
@@ -0,0 +1,113 @@
+bun test v1.3.12 (700fc117)
+
+packages/prompts-core/src/variant-resolver.test.ts:
+S1 actual: __red__
+27 |       // when
+28 |       const actual = resolveVariant({ modelID: "claude-opus-4-7", variants })
+29 | 
+30 |       // then
+31 |       console.info("S1 actual:", actual)
+32 |       expect(actual).toBe("default")
+                          ^
+error: expect(received).toBe(expected)
+
+Expected: "default"
+Received: "__red__"
+
+      at <anonymous> (/Users/yeongyu/local-workspaces/omo-wt/feat/prompts-core-foundation/packages/prompts-core/src/variant-resolver.test.ts:32:22)
+(fail) resolveVariant > #given declared model variants > #when claude opus has no model match #then returns default fallback [0.39ms]
+S2 actual: __red__
+43 |       // when
+44 |       const actual = resolveVariant({ modelID: "openai/gpt-5.5", variants })
+45 | 
+46 |       // then
+47 |       console.info("S2 actual:", actual)
+48 |       expect(actual).toBe("gpt")
+                          ^
+error: expect(received).toBe(expected)
+
+Expected: "gpt"
+Received: "__red__"
+
+      at <anonymous> (/Users/yeongyu/local-workspaces/omo-wt/feat/prompts-core-foundation/packages/prompts-core/src/variant-resolver.test.ts:48:22)
+(fail) resolveVariant > #given declared model variants > #when openai gpt model matches #then returns gpt [0.10ms]
+S3 actual: __red__
+59 |       // when
+60 |       const actual = resolveVariant({ modelID: "google/gemini-3-1-pro", variants })
+61 | 
+62 |       // then
+63 |       console.info("S3 actual:", actual)
+64 |       expect(actual).toBe("gemini")
+                          ^
+error: expect(received).toBe(expected)
+
+Expected: "gemini"
+Received: "__red__"
+
+      at <anonymous> (/Users/yeongyu/local-workspaces/omo-wt/feat/prompts-core-foundation/packages/prompts-core/src/variant-resolver.test.ts:64:22)
+(fail) resolveVariant > #given declared model variants > #when google gemini model matches #then returns gemini [0.04ms]
+S4 actual: __red__
+80 |         variants,
+81 |       })
+82 | 
+83 |       // then
+84 |       console.info("S4 actual:", actual)
+85 |       expect(actual).toBe("planner")
+                          ^
+error: expect(received).toBe(expected)
+
+Expected: "planner"
+Received: "__red__"
+
+      at <anonymous> (/Users/yeongyu/local-workspaces/omo-wt/feat/prompts-core-foundation/packages/prompts-core/src/variant-resolver.test.ts:85:22)
+(fail) resolveVariant > #given agent and fallback variants > #when agent and model both match #then declared agent variant wins [0.12ms]
+S5 actual: __red__
+94 |       // when
+95 |       const actual = resolveVariant({ variants })
+96 | 
+97 |       // then
+98 |       console.info("S5 actual:", actual)
+99 |       expect(actual).toBe("default")
+                          ^
+error: expect(received).toBe(expected)
+
+Expected: "default"
+Received: "__red__"
+
+      at <anonymous> (/Users/yeongyu/local-workspaces/omo-wt/feat/prompts-core-foundation/packages/prompts-core/src/variant-resolver.test.ts:99:22)
+(fail) resolveVariant > #given agent and fallback variants > #when no context is provided #then returns default fallback [0.08ms]
+S6 actual: __red__
+109 |       // when
+110 |       const actual = resolveVariant({ modelID: "unknown-model", variants })
+111 | 
+112 |       // then
+113 |       console.info("S6 actual:", actual)
+114 |       expect(actual).toBe("default")
+                           ^
+error: expect(received).toBe(expected)
+
+Expected: "default"
+Received: "__red__"
+
+      at <anonymous> (/Users/yeongyu/local-workspaces/omo-wt/feat/prompts-core-foundation/packages/prompts-core/src/variant-resolver.test.ts:114:22)
+(fail) resolveVariant > #given agent and fallback variants > #when no variant test matches #then returns fallback [0.07ms]
+S7 actual: __red__
+134 |         }
+135 |       }
+136 |       console.info("S7 actual:", actual)
+137 | 
+138 |       // then
+139 |       expect(thrown).toBeInstanceOf(NoMatchingVariantError)
+                           ^
+error: expect(received).toBeInstanceOf(expected)
+
+Expected constructor: [class NoMatchingVariantError extends Error]
+Received value: undefined
+
+      at <anonymous> (/Users/yeongyu/local-workspaces/omo-wt/feat/prompts-core-foundation/packages/prompts-core/src/variant-resolver.test.ts:139:22)
+(fail) resolveVariant > #given agent and fallback variants > #when no variant matches and no fallback exists #then throws [0.09ms]
+
+ 0 pass
+ 7 fail
+ 7 expect() calls
+Ran 7 tests across 1 file. [74.00ms]
diff --git a/.omo/evidence/pr1-prompts-core/s6.red.log b/.omo/evidence/pr1-prompts-core/s6.red.log
new file mode 100644
index 000000000..e6577d62b
--- /dev/null
+++ b/.omo/evidence/pr1-prompts-core/s6.red.log
@@ -0,0 +1,113 @@
+bun test v1.3.12 (700fc117)
+
+packages/prompts-core/src/variant-resolver.test.ts:
+S1 actual: __red__
+27 |       // when
+28 |       const actual = resolveVariant({ modelID: "claude-opus-4-7", variants })
+29 | 
+30 |       // then
+31 |       console.info("S1 actual:", actual)
+32 |       expect(actual).toBe("default")
+                          ^
+error: expect(received).toBe(expected)
+
+Expected: "default"
+Received: "__red__"
+
+      at <anonymous> (/Users/yeongyu/local-workspaces/omo-wt/feat/prompts-core-foundation/packages/prompts-core/src/variant-resolver.test.ts:32:22)
+(fail) resolveVariant > #given declared model variants > #when claude opus has no model match #then returns default fallback [0.39ms]
+S2 actual: __red__
+43 |       // when
+44 |       const actual = resolveVariant({ modelID: "openai/gpt-5.5", variants })
+45 | 
+46 |       // then
+47 |       console.info("S2 actual:", actual)
+48 |       expect(actual).toBe("gpt")
+                          ^
+error: expect(received).toBe(expected)
+
+Expected: "gpt"
+Received: "__red__"
+
+      at <anonymous> (/Users/yeongyu/local-workspaces/omo-wt/feat/prompts-core-foundation/packages/prompts-core/src/variant-resolver.test.ts:48:22)
+(fail) resolveVariant > #given declared model variants > #when openai gpt model matches #then returns gpt [0.10ms]
+S3 actual: __red__
+59 |       // when
+60 |       const actual = resolveVariant({ modelID: "google/gemini-3-1-pro", variants })
+61 | 
+62 |       // then
+63 |       console.info("S3 actual:", actual)
+64 |       expect(actual).toBe("gemini")
+                          ^
+error: expect(received).toBe(expected)
+
+Expected: "gemini"
+Received: "__red__"
+
+      at <anonymous> (/Users/yeongyu/local-workspaces/omo-wt/feat/prompts-core-foundation/packages/prompts-core/src/variant-resolver.test.ts:64:22)
+(fail) resolveVariant > #given declared model variants > #when google gemini model matches #then returns gemini [0.04ms]
+S4 actual: __red__
+80 |         variants,
+81 |       })
+82 | 
+83 |       // then
+84 |       console.info("S4 actual:", actual)
+85 |       expect(actual).toBe("planner")
+                          ^
+error: expect(received).toBe(expected)
+
+Expected: "planner"
+Received: "__red__"
+
+      at <anonymous> (/Users/yeongyu/local-workspaces/omo-wt/feat/prompts-core-foundation/packages/prompts-core/src/variant-resolver.test.ts:85:22)
+(fail) resolveVariant > #given agent and fallback variants > #when agent and model both match #then declared agent variant wins [0.12ms]
+S5 actual: __red__
+94 |       // when
+95 |       const actual = resolveVariant({ variants })
+96 | 
+97 |       // then
+98 |       console.info("S5 actual:", actual)
+99 |       expect(actual).toBe("default")
+                          ^
+error: expect(received).toBe(expected)
+
+Expected: "default"
+Received: "__red__"
+
+      at <anonymous> (/Users/yeongyu/local-workspaces/omo-wt/feat/prompts-core-foundation/packages/prompts-core/src/variant-resolver.test.ts:99:22)
+(fail) resolveVariant > #given agent and fallback variants > #when no context is provided #then returns default fallback [0.08ms]
+S6 actual: __red__
+109 |       // when
+110 |       const actual = resolveVariant({ modelID: "unknown-model", variants })
+111 | 
+112 |       // then
+113 |       console.info("S6 actual:", actual)
+114 |       expect(actual).toBe("default")
+                           ^
+error: expect(received).toBe(expected)
+
+Expected: "default"
+Received: "__red__"
+
+      at <anonymous> (/Users/yeongyu/local-workspaces/omo-wt/feat/prompts-core-foundation/packages/prompts-core/src/variant-resolver.test.ts:114:22)
+(fail) resolveVariant > #given agent and fallback variants > #when no variant test matches #then returns fallback [0.07ms]
+S7 actual: __red__
+134 |         }
+135 |       }
+136 |       console.info("S7 actual:", actual)
+137 | 
+138 |       // then
+139 |       expect(thrown).toBeInstanceOf(NoMatchingVariantError)
+                           ^
+error: expect(received).toBeInstanceOf(expected)
+
+Expected constructor: [class NoMatchingVariantError extends Error]
+Received value: undefined
+
+      at <anonymous> (/Users/yeongyu/local-workspaces/omo-wt/feat/prompts-core-foundation/packages/prompts-core/src/variant-resolver.test.ts:139:22)
+(fail) resolveVariant > #given agent and fallback variants > #when no variant matches and no fallback exists #then throws [0.09ms]
+
+ 0 pass
+ 7 fail
+ 7 expect() calls
+Ran 7 tests across 1 file. [74.00ms]
diff --git a/.omo/evidence/pr1-prompts-core/s7.red.log b/.omo/evidence/pr1-prompts-core/s7.red.log
new file mode 100644
index 000000000..e6577d62b
--- /dev/null
+++ b/.omo/evidence/pr1-prompts-core/s7.red.log
@@ -0,0 +1,113 @@
+bun test v1.3.12 (700fc117)
+
+packages/prompts-core/src/variant-resolver.test.ts:
+S1 actual: __red__
+27 |       // when
+28 |       const actual = resolveVariant({ modelID: "claude-opus-4-7", variants })
+29 | 
+30 |       // then
+31 |       console.info("S1 actual:", actual)
+32 |       expect(actual).toBe("default")
+                          ^
+error: expect(received).toBe(expected)
+
+Expected: "default"
+Received: "__red__"
+
+      at <anonymous> (/Users/yeongyu/local-workspaces/omo-wt/feat/prompts-core-foundation/packages/prompts-core/src/variant-resolver.test.ts:32:22)
+(fail) resolveVariant > #given declared model variants > #when claude opus has no model match #then returns default fallback [0.39ms]
+S2 actual: __red__
+43 |       // when
+44 |       const actual = resolveVariant({ modelID: "openai/gpt-5.5", variants })
+45 | 
+46 |       // then
+47 |       console.info("S2 actual:", actual)
+48 |       expect(actual).toBe("gpt")
+                          ^
+error: expect(received).toBe(expected)
+
+Expected: "gpt"
+Received: "__red__"
+
+      at <anonymous> (/Users/yeongyu/local-workspaces/omo-wt/feat/prompts-core-foundation/packages/prompts-core/src/variant-resolver.test.ts:48:22)
+(fail) resolveVariant > #given declared model variants > #when openai gpt model matches #then returns gpt [0.10ms]
+S3 actual: __red__
+59 |       // when
+60 |       const actual = resolveVariant({ modelID: "google/gemini-3-1-pro", variants })
+61 | 
+62 |       // then
+63 |       console.info("S3 actual:", actual)
+64 |       expect(actual).toBe("gemini")
+                          ^
+error: expect(received).toBe(expected)
+
+Expected: "gemini"
+Received: "__red__"
+
+      at <anonymous> (/Users/yeongyu/local-workspaces/omo-wt/feat/prompts-core-foundation/packages/prompts-core/src/variant-resolver.test.ts:64:22)
+(fail) resolveVariant > #given declared model variants > #when google gemini model matches #then returns gemini [0.04ms]
+S4 actual: __red__
+80 |         variants,
+81 |       })
+82 | 
+83 |       // then
+84 |       console.info("S4 actual:", actual)
+85 |       expect(actual).toBe("planner")
+                          ^
+error: expect(received).toBe(expected)
+
+Expected: "planner"
+Received: "__red__"
+
+      at <anonymous> (/Users/yeongyu/local-workspaces/omo-wt/feat/prompts-core-foundation/packages/prompts-core/src/variant-resolver.test.ts:85:22)
+(fail) resolveVariant > #given agent and fallback variants > #when agent and model both match #then declared agent variant wins [0.12ms]
+S5 actual: __red__
+94 |       // when
+95 |       const actual = resolveVariant({ variants })
+96 | 
+97 |       // then
+98 |       console.info("S5 actual:", actual)
+99 |       expect(actual).toBe("default")
+                          ^
+error: expect(received).toBe(expected)
+
+Expected: "default"
+Received: "__red__"
+
+      at <anonymous> (/Users/yeongyu/local-workspaces/omo-wt/feat/prompts-core-foundation/packages/prompts-core/src/variant-resolver.test.ts:99:22)
+(fail) resolveVariant > #given agent and fallback variants > #when no context is provided #then returns default fallback [0.08ms]
+S6 actual: __red__
+109 |       // when
+110 |       const actual = resolveVariant({ modelID: "unknown-model", variants })
+111 | 
+112 |       // then
+113 |       console.info("S6 actual:", actual)
+114 |       expect(actual).toBe("default")
+                           ^
+error: expect(received).toBe(expected)
+
+Expected: "default"
+Received: "__red__"
+
+      at <anonymous> (/Users/yeongyu/local-workspaces/omo-wt/feat/prompts-core-foundation/packages/prompts-core/src/variant-resolver.test.ts:114:22)
+(fail) resolveVariant > #given agent and fallback variants > #when no variant test matches #then returns fallback [0.07ms]
+S7 actual: __red__
+134 |         }
+135 |       }
+136 |       console.info("S7 actual:", actual)
+137 | 
+138 |       // then
+139 |       expect(thrown).toBeInstanceOf(NoMatchingVariantError)
+                           ^
+error: expect(received).toBeInstanceOf(expected)
+
+Expected constructor: [class NoMatchingVariantError extends Error]
+Received value: undefined
+
+      at <anonymous> (/Users/yeongyu/local-workspaces/omo-wt/feat/prompts-core-foundation/packages/prompts-core/src/variant-resolver.test.ts:139:22)
+(fail) resolveVariant > #given agent and fallback variants > #when no variant matches and no fallback exists #then throws [0.09ms]
+
+ 0 pass
+ 7 fail
+ 7 expect() calls
+Ran 7 tests across 1 file. [74.00ms]
diff --git a/.omo/evidence/pr1-prompts-core/variant-resolver.red.log b/.omo/evidence/pr1-prompts-core/variant-resolver.red.log
new file mode 100644
index 000000000..e6577d62b
--- /dev/null
+++ b/.omo/evidence/pr1-prompts-core/variant-resolver.red.log
@@ -0,0 +1,113 @@
+bun test v1.3.12 (700fc117)
+
+packages/prompts-core/src/variant-resolver.test.ts:
+S1 actual: __red__
+27 |       // when
+28 |       const actual = resolveVariant({ modelID: "claude-opus-4-7", variants })
+29 | 
+30 |       // then
+31 |       console.info("S1 actual:", actual)
+32 |       expect(actual).toBe("default")
+                          ^
+error: expect(received).toBe(expected)
+
+Expected: "default"
+Received: "__red__"
+
+      at <anonymous> (/Users/yeongyu/local-workspaces/omo-wt/feat/prompts-core-foundation/packages/prompts-core/src/variant-resolver.test.ts:32:22)
+(fail) resolveVariant > #given declared model variants > #when claude opus has no model match #then returns default fallback [0.39ms]
+S2 actual: __red__
+43 |       // when
+44 |       const actual = resolveVariant({ modelID: "openai/gpt-5.5", variants })
+45 | 
+46 |       // then
+47 |       console.info("S2 actual:", actual)
+48 |       expect(actual).toBe("gpt")
+                          ^
+error: expect(received).toBe(expected)
+
+Expected: "gpt"
+Received: "__red__"
+
+      at <anonymous> (/Users/yeongyu/local-workspaces/omo-wt/feat/prompts-core-foundation/packages/prompts-core/src/variant-resolver.test.ts:48:22)
+(fail) resolveVariant > #given declared model variants > #when openai gpt model matches #then returns gpt [0.10ms]
+S3 actual: __red__
+59 |       // when
+60 |       const actual = resolveVariant({ modelID: "google/gemini-3-1-pro", variants })
+61 | 
+62 |       // then
+63 |       console.info("S3 actual:", actual)
+64 |       expect(actual).toBe("gemini")
+                          ^
+error: expect(received).toBe(expected)
+
+Expected: "gemini"
+Received: "__red__"
+
+      at <anonymous> (/Users/yeongyu/local-workspaces/omo-wt/feat/prompts-core-foundation/packages/prompts-core/src/variant-resolver.test.ts:64:22)
+(fail) resolveVariant > #given declared model variants > #when google gemini model matches #then returns gemini [0.04ms]
+S4 actual: __red__
+80 |         variants,
+81 |       })
+82 | 
+83 |       // then
+84 |       console.info("S4 actual:", actual)
+85 |       expect(actual).toBe("planner")
+                          ^
+error: expect(received).toBe(expected)
+
+Expected: "planner"
+Received: "__red__"
+
+      at <anonymous> (/Users/yeongyu/local-workspaces/omo-wt/feat/prompts-core-foundation/packages/prompts-core/src/variant-resolver.test.ts:85:22)
+(fail) resolveVariant > #given agent and fallback variants > #when agent and model both match #then declared agent variant wins [0.12ms]
+S5 actual: __red__
+94 |       // when
+95 |       const actual = resolveVariant({ variants })
+96 | 
+97 |       // then
+98 |       console.info("S5 actual:", actual)
+99 |       expect(actual).toBe("default")
+                          ^
+error: expect(received).toBe(expected)
+
+Expected: "default"
+Received: "__red__"
+
+      at <anonymous> (/Users/yeongyu/local-workspaces/omo-wt/feat/prompts-core-foundation/packages/prompts-core/src/variant-resolver.test.ts:99:22)
+(fail) resolveVariant > #given agent and fallback variants > #when no context is provided #then returns default fallback [0.08ms]
+S6 actual: __red__
+109 |       // when
+110 |       const actual = resolveVariant({ modelID: "unknown-model", variants })
+111 | 
+112 |       // then
+113 |       console.info("S6 actual:", actual)
+114 |       expect(actual).toBe("default")
+                           ^
+error: expect(received).toBe(expected)
+
+Expected: "default"
+Received: "__red__"
+
+      at <anonymous> (/Users/yeongyu/local-workspaces/omo-wt/feat/prompts-core-foundation/packages/prompts-core/src/variant-resolver.test.ts:114:22)
+(fail) resolveVariant > #given agent and fallback variants > #when no variant test matches #then returns fallback [0.07ms]
+S7 actual: __red__
+134 |         }
+135 |       }
+136 |       console.info("S7 actual:", actual)
+137 | 
+138 |       // then
+139 |       expect(thrown).toBeInstanceOf(NoMatchingVariantError)
+                           ^
+error: expect(received).toBeInstanceOf(expected)
+
+Expected constructor: [class NoMatchingVariantError extends Error]
+Received value: undefined
+
+      at <anonymous> (/Users/yeongyu/local-workspaces/omo-wt/feat/prompts-core-foundation/packages/prompts-core/src/variant-resolver.test.ts:139:22)
+(fail) resolveVariant > #given agent and fallback variants > #when no variant matches and no fallback exists #then throws [0.09ms]
+
+ 0 pass
+ 7 fail
+ 7 expect() calls
+Ran 7 tests across 1 file. [74.00ms]
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..ec3c0c466
--- /dev/null
+++ b/packages/prompts-core/src/variant-resolver.test.ts
@@ -0,0 +1,142 @@
+import { describe, expect, test } from "bun:test"
+
+import { resolveVariant } from "./variant-resolver"
+import { NoMatchingVariantError, type VariantTable } from "./types"
+
+const isGpt = (input: { modelID?: string; agentName?: string }): boolean =>
+  input.modelID?.includes("gpt") ?? false
+
+const isGemini = (input: { modelID?: string; agentName?: string }): boolean =>
+  input.modelID?.includes("gemini") ?? false
+
+const isPlanner = (input: { modelID?: string; agentName?: string }): boolean =>
+  input.agentName === "prometheus"
+
+const alwaysFalse = (): boolean => false
+
+describe("resolveVariant", () => {
+  describe("#given declared model variants", () => {
+    test("#when claude opus has no model match #then returns default fallback", () => {
+      // given
+      const variants = {
+        gpt: { test: isGpt },
+        gemini: { test: isGemini },
+        default: { fallback: true },
+      } satisfies VariantTable
+
+      // when
+      const actual = resolveVariant({ modelID: "claude-opus-4-7", variants })
+
+      // then
+      console.info("S1 actual:", actual)
+      expect(actual).toBe("default")
+    })
+
+    test("#when openai gpt model matches #then returns gpt", () => {
+      // given
+      const variants = {
+        gpt: { test: isGpt },
+        gemini: { test: isGemini },
+        default: { fallback: true },
+      } satisfies VariantTable
+
+      // when
+      const actual = resolveVariant({ modelID: "openai/gpt-5.5", variants })
+
+      // then
+      console.info("S2 actual:", actual)
+      expect(actual).toBe("gpt")
+    })
+
+    test("#when google gemini model matches #then returns gemini", () => {
+      // given
+      const variants = {
+        gpt: { test: isGpt },
+        gemini: { test: isGemini },
+        default: { fallback: true },
+      } satisfies VariantTable
+
+      // when
+      const actual = resolveVariant({ modelID: "google/gemini-3-1-pro", variants })
+
+      // then
+      console.info("S3 actual:", actual)
+      expect(actual).toBe("gemini")
+    })
+  })
+
+  describe("#given agent and fallback variants", () => {
+    test("#when agent and model both match #then declared agent variant wins", () => {
+      // given
+      const variants = {
+        planner: { test: isPlanner },
+        gpt: { test: isGpt },
+      } satisfies VariantTable
+
+      // when
+      const actual = resolveVariant({
+        agentName: "prometheus",
+        modelID: "openai/gpt-5.5",
+        variants,
+      })
+
+      // then
+      console.info("S4 actual:", actual)
+      expect(actual).toBe("planner")
+    })
+
+    test("#when no context is provided #then returns default fallback", () => {
+      // given
+      const variants = {
+        default: { fallback: true },
+      } satisfies VariantTable
+
+      // when
+      const actual = resolveVariant({ variants })
+
+      // then
+      console.info("S5 actual:", actual)
+      expect(actual).toBe("default")
+    })
+
+    test("#when no variant test matches #then returns fallback", () => {
+      // given
+      const variants = {
+        gpt: { test: alwaysFalse },
+        default: { fallback: true },
+      } satisfies VariantTable
+
+      // when
+      const actual = resolveVariant({ modelID: "unknown-model", variants })
+
+      // then
+      console.info("S6 actual:", actual)
+      expect(actual).toBe("default")
+    })
+
+    test("#when no variant matches and no fallback exists #then throws", () => {
+      // given
+      const variants = {
+        a: { test: alwaysFalse },
+      } satisfies VariantTable
+
+      // when
+      let actual = "no throw"
+      let thrown: unknown
+      try {
+        actual = resolveVariant({ modelID: "x", variants })
+      } catch (error) {
+        thrown = error
+        if (error instanceof Error) {
+          actual = error.name
+        } else {
+          throw error
+        }
+      }
+      console.info("S7 actual:", actual)
+
+      // then
+      expect(thrown).toBeInstanceOf(NoMatchingVariantError)
+    })
+  })
+})
diff --git a/packages/prompts-core/src/variant-resolver.ts b/packages/prompts-core/src/variant-resolver.ts
new file mode 100644
index 000000000..f836821fa
--- /dev/null
+++ b/packages/prompts-core/src/variant-resolver.ts
@@ -0,0 +1,5 @@
+import type { ResolveVariantInput } from "./types"
+
+export function resolveVariant(_input: ResolveVariantInput): string {
+  return "__red__"
+}