diff --git a/packages/adapters/opencode-local/src/index.ts b/packages/adapters/opencode-local/src/index.ts
index 0c16e2d8..67fbdb4b 100644
--- a/packages/adapters/opencode-local/src/index.ts
+++ b/packages/adapters/opencode-local/src/index.ts
@@ -37,4 +37,7 @@ Notes:
 - Paperclip requires an explicit \`model\` value for \`opencode_local\` agents.
 - Runs are executed with: opencode run --format json ...
 - Sessions are resumed with --session when stored session cwd matches current cwd.
+- The adapter sets OPENCODE_DISABLE_PROJECT_CONFIG=true to prevent OpenCode from \
+  writing an opencode.json config file into the project working directory. Model \
+  selection is passed via the --model CLI flag instead.
 `;
diff --git a/packages/adapters/opencode-local/src/server/execute.ts b/packages/adapters/opencode-local/src/server/execute.ts
index 09db7337..788ad835 100644
--- a/packages/adapters/opencode-local/src/server/execute.ts
+++ b/packages/adapters/opencode-local/src/server/execute.ts
@@ -169,6 +169,11 @@ export async function execute(ctx: AdapterExecutionContext): Promise<AdapterExec
   for (const [key, value] of Object.entries(envConfig)) {
     if (typeof value === "string") env[key] = value;
   }
+  // Prevent OpenCode from writing an opencode.json config file into the
+  // project working directory (which would pollute the git repo).  Model
+  // selection is already handled via the --model CLI flag.  Set after the
+  // envConfig loop so user overrides cannot disable this guard.
+  env.OPENCODE_DISABLE_PROJECT_CONFIG = "true";
   if (!hasExplicitApiKey && authToken) {
     env.PAPERCLIP_API_KEY = authToken;
   }
diff --git a/packages/adapters/opencode-local/src/server/models.ts b/packages/adapters/opencode-local/src/server/models.ts
index 94634d86..95cb1fc9 100644
--- a/packages/adapters/opencode-local/src/server/models.ts
+++ b/packages/adapters/opencode-local/src/server/models.ts
@@ -120,7 +120,8 @@ export async function discoverOpenCodeModels(input: {
     // /etc/passwd entry (e.g. `docker run --user 1234` with a minimal
     // image). Fall back to process.env.HOME.
   }
-  const runtimeEnv = normalizeEnv(ensurePathInEnv({ ...process.env, ...env, ...(resolvedHome ? { HOME: resolvedHome } : {}) }));
+  // Prevent OpenCode from writing an opencode.json into the working directory.
+  const runtimeEnv = normalizeEnv(ensurePathInEnv({ ...process.env, ...env, ...(resolvedHome ? { HOME: resolvedHome } : {}), OPENCODE_DISABLE_PROJECT_CONFIG: "true" }));
 
   const result = await runChildProcess(
     `opencode-models-${Date.now()}-${Math.random().toString(16).slice(2)}`,
diff --git a/packages/adapters/opencode-local/src/server/test.ts b/packages/adapters/opencode-local/src/server/test.ts
index 5bb7aa36..ad3957d1 100644
--- a/packages/adapters/opencode-local/src/server/test.ts
+++ b/packages/adapters/opencode-local/src/server/test.ts
@@ -90,6 +90,8 @@ export async function testEnvironment(
     });
   }
 
+  // Prevent OpenCode from writing an opencode.json into the working directory.
+  env.OPENCODE_DISABLE_PROJECT_CONFIG = "true";
   const runtimeEnv = normalizeEnv(ensurePathInEnv({ ...process.env, ...env }));
 
   const cwdInvalid = checks.some((check) => check.code === "opencode_cwd_invalid");