diff --git a/src/core/command-generation/adapters/opencode.ts b/src/core/command-generation/adapters/opencode.ts
index 74f645022e..b3d96d63e5 100644
--- a/src/core/command-generation/adapters/opencode.ts
+++ b/src/core/command-generation/adapters/opencode.ts
@@ -8,10 +8,27 @@ import path from 'path';
 import type { CommandContent, ToolCommandAdapter } from '../types.js';
 import { escapeYamlValue } from '../yaml.js';
 
+const OPENCODE_INPUT_BLOCK = /^\*\*Input\*\*:[^\r\n]*(?:\r?\n(?!\r?\n)[^\r\n]*)*/m;
+const OPENCODE_NO_INPUT = /^\*\*Input\*\*:\s*None required\b/im;
+const OPENCODE_ARGUMENT_PLACEHOLDER = /\$(?:ARGUMENTS\b|[1-9]\d*\b)/;
+
+function injectOpenCodeArgs(body: string): string {
+  if (OPENCODE_ARGUMENT_PLACEHOLDER.test(body) || OPENCODE_NO_INPUT.test(body)) {
+    return body;
+  }
+
+  const eol = body.includes('\r\n') ? '\r\n' : '\n';
+  return body.replace(
+    OPENCODE_INPUT_BLOCK,
+    (input) => `${input}${eol}**Provided arguments**: $ARGUMENTS`
+  );
+}
+
 /**
  * OpenCode adapter for command generation.
  * File path: .opencode/commands/opsx-<id>.md
- * Frontmatter: description
+ * Frontmatter: description. $ARGUMENTS is injected after the complete input
+ * contract because OpenCode only passes arguments through explicit placeholders.
  */
 export const opencodeAdapter: ToolCommandAdapter = {
   toolId: 'opencode',
@@ -25,7 +42,7 @@ export const opencodeAdapter: ToolCommandAdapter = {
 description: ${escapeYamlValue(content.description)}
 ---
 
-${content.body}
+${injectOpenCodeArgs(content.body)}
 `;
   },
 };
diff --git a/test/core/command-generation/adapters.test.ts b/test/core/command-generation/adapters.test.ts
index b4dd55459b..9036a239a4 100644
--- a/test/core/command-generation/adapters.test.ts
+++ b/test/core/command-generation/adapters.test.ts
@@ -607,6 +607,69 @@ describe('command-generation/adapters', () => {
       expect(output).toContain('This is the command body.');
     });
 
+    it('should pass invocation arguments into the OpenSpec input contract', () => {
+      const output = opencodeAdapter.formatFile({
+        ...sampleContent,
+        body: '# OpenSpec command\n\n**Input**: A change name or description.\n\nRun the workflow.',
+      });
+      expect(output).toContain(
+        '**Input**: A change name or description.\n**Provided arguments**: $ARGUMENTS'
+      );
+    });
+
+    it('should not duplicate an existing $ARGUMENTS placeholder', () => {
+      const output = opencodeAdapter.formatFile({
+        ...sampleContent,
+        body: '**Input**: A change name.\nExisting input: $ARGUMENTS',
+      });
+      expect(output.match(/\$ARGUMENTS/g)).toHaveLength(1);
+    });
+
+    it('should not duplicate documented positional argument placeholders', () => {
+      const output = opencodeAdapter.formatFile({
+        ...sampleContent,
+        body: '**Input**: Two values.\nFirst: $1\nSecond: $2',
+      });
+      expect(output).not.toContain('**Provided arguments**: $ARGUMENTS');
+      expect(output).toContain('First: $1\nSecond: $2');
+    });
+
+    it('should keep multi-line input guidance together before provided arguments', () => {
+      const output = opencodeAdapter.formatFile({
+        ...sampleContent,
+        body: '**Input**: A topic, such as:\n- an idea\n- a problem\n\n**Steps**\n1. Explore.',
+      });
+      expect(output).toContain(
+        '**Input**: A topic, such as:\n- an idea\n- a problem\n**Provided arguments**: $ARGUMENTS'
+      );
+    });
+
+    it('should preserve CRLF while keeping multi-line input guidance together', () => {
+      const output = opencodeAdapter.formatFile({
+        ...sampleContent,
+        body: '**Input**: A topic, such as:\r\n- an idea\r\n- a problem\r\n\r\nRun it.',
+      });
+      expect(output).toContain(
+        '**Input**: A topic, such as:\r\n- an idea\r\n- a problem\r\n**Provided arguments**: $ARGUMENTS\r\n\r\nRun it.'
+      );
+    });
+
+    it('should not add invocation arguments to an explicitly input-free workflow', () => {
+      const output = opencodeAdapter.formatFile({
+        ...sampleContent,
+        body: '**Input**: None required (prompts for selection)\n\nPrompt the user.',
+      });
+      expect(output).not.toContain('$ARGUMENTS');
+    });
+
+    it('should preserve exactly one argument placeholder for each workflow that accepts input', () => {
+      for (const content of getCommandContents()) {
+        const output = generateCommand(content, opencodeAdapter).fileContent;
+        const acceptsInput = /^\*\*Input\*\*:(?!\s*None required\b)/im.test(content.body);
+        expect(output.match(/\$ARGUMENTS/g) ?? [], content.id).toHaveLength(acceptsInput ? 1 : 0);
+      }
+    });
+
     it('is generated by generateCommand with hyphen command references', () => {
       const contentWithCommands: CommandContent = {
         ...sampleContent,
diff --git a/test/core/init.test.ts b/test/core/init.test.ts
index 42a60a79f6..f5930bd858 100644
--- a/test/core/init.test.ts
+++ b/test/core/init.test.ts
@@ -1349,6 +1349,8 @@ describe('InitCommand - profile and detection features', () => {
     // New commands should be at the correct plural path
     const newCommandsDir = path.join(testDir, '.opencode', 'commands');
     expect(await directoryExists(newCommandsDir)).toBe(true);
+    const proposeCommand = await fs.readFile(path.join(newCommandsDir, 'opsx-propose.md'), 'utf-8');
+    expect(proposeCommand).toContain('**Provided arguments**: $ARGUMENTS');
   });
 
   it('should remove managed global Codex prompts in non-interactive mode', async () => {
diff --git a/test/core/update.test.ts b/test/core/update.test.ts
index b541bdadc1..b385abe1f2 100644
--- a/test/core/update.test.ts
+++ b/test/core/update.test.ts
@@ -1332,6 +1332,46 @@ metadata:
       expect(content).toContain('**Provided arguments**: $ARGUMENTS');
     });
 
+    it('should repair stale OpenCode commands-only installs once', async () => {
+      setMockConfig({ featureFlags: {}, profile: 'core', delivery: 'commands' });
+      const commandsDir = path.join(testDir, '.opencode', 'commands');
+      const coreCommandIds = [
+        'explore',
+        'apply',
+        'update',
+        'sync',
+        'archive',
+        'propose',
+      ];
+      await fs.mkdir(commandsDir, { recursive: true });
+      for (const commandId of coreCommandIds) {
+        await fs.writeFile(
+          path.join(commandsDir, `opsx-${commandId}.md`),
+          'old command without arguments'
+        );
+      }
+
+      await updateCommand.execute(testDir);
+
+      for (const commandId of coreCommandIds) {
+        const content = await fs.readFile(
+          path.join(commandsDir, `opsx-${commandId}.md`),
+          'utf-8'
+        );
+        expect(content.match(/\$ARGUMENTS/g)).toHaveLength(1);
+        expect(content).toContain('**Provided arguments**: $ARGUMENTS');
+        expect(content).not.toContain('old command without arguments');
+      }
+
+      const consoleSpy = vi.spyOn(console, 'log');
+      await updateCommand.execute(testDir);
+
+      const logCalls = consoleSpy.mock.calls.flat().map(String);
+      expect(logCalls.some((entry) => entry.includes('up to date'))).toBe(true);
+      expect(logCalls.some((entry) => entry.includes('Updating 1 tool(s)'))).toBe(false);
+      consoleSpy.mockRestore();
+    });
+
     it('should migrate a legacy .windsurf install to .devin, preserving user files', async () => {
       // A project set up before the Devin Desktop rebrand: OpenSpec skills and
       // workflows under .windsurf/, alongside files the user wrote themselves.