Update spec.md

Author: ajuan-muchen

openspec/specs/cli-update/spec.md

@@ -69,7 +69,7 @@ The update command SHALL refresh existing slash command files for configured too
 - **AND** ensure templates include instructions for the relevant workflow stage
 
 #### Scenario: Updating slash commands for Continue
-- **WHEN** `.continue/prompts/` contains `openspec-proposal.md`, `openspec-apply.md`, and `openspec-archive.md`
+- **WHEN** `.continue/prompts/` contains `openspec-proposal.prompt`, `openspec-apply.prompt`, and `openspec-archive.prompt`
 - **THEN** refresh each file using shared templates
 - **AND** ensure templates include instructions for the relevant workflow stage