[Fix] Agents identify as OpenCode before Roomote

[roomote-roomote]

​Opened on behalf of @daniel-lxs. Follow up by mentioning @roomote-roomote, in the web UI, or in Slack.

What changed

• Add a system-transform hook that removes only OpenCode's leading You are OpenCode, identity prefix.
• Install the same hook in Fast's managed OpenCode server and standard task sandboxes.
• Cover uppercase and lowercase identity variants while proving non-leading and Roomote prompt text stays unchanged.

Why this change was made

OpenCode prepends its own product identity before Roomote's Fast and standard task prompt layers. Removing that prefix at the final system-prompt transform point avoids conflicting product identities without rewriting either mode's existing behavior instructions.

Impact

Fast and standard agents retain their existing Roomote prompt copy, engineering guidance, workflow rules, and tool behavior byte-for-byte. Focused plugin and runtime tests, package type checks, formatting, and the repository pre-push suite pass.

[roomote-community]

No actionable code issues found. See task

• Fast sessions using a configured external OpenCode SDK server bypass the identity transform (packages/cloud-agents/src/server/opencode-runtime.ts:255). — dismissed: Fast passes useConfiguredServer: false, and the existing configured-URL regression test confirms a managed server is spawned.

_{Reviewed 50e9f05}

[roomote-roomote]

Cleaned the PR to remove only OpenCode's leading identity prefix. Existing Roomote Fast, standard, and shared-style prompt copy is unchanged in the net diff. Focused tests, package type checks, formatting, and pre-push checks pass in 7c784bf.

[roomote-roomote]

@roomote-roomote rerun the review against the unchanged head. The only prior finding was dismissed with call-chain and regression-test evidence in the resolved thread.

[daniel-lxs]

@roomote-roomote please rerun the code review on the unchanged head. The prior configured-server finding was dismissed with the Fast call-chain and existing regression-test evidence; verify the current seven-file diff for any remaining actionable issues.