#19200: fix(cli): validate --session-id is not a session key format

When users pass a session key format (`agent:...`) to `--session-id`, show a helpful error message directing them to use `--session-key` instead. ## Problem Users sometimes confuse `--session-id` (for UUIDs) with `--session-key` (for `agent:...` format keys), leading to unexpected behavior where the agent workspace is not resolved correctly. ## Solution Add validation that detects when a session key format is passed to `--session-id` and throws a clear error: ``` It looks like you passed a session key to --session-id. Please use --session-key instead. ``` This teaches users the correct parameter usage rather than silently accepting both formats. Closes #13635 <!-- greptile_comment --> <h3>Greptile Summary</h3> Adds input validation to the `agentCommand` function in `src/commands/agent.ts` that detects when a session key format (`agent:...`) is mistakenly passed to `--session-id` and throws a descriptive error directing users to use `--session-key` instead. - The validation check at line 194 uses `.trim().toLowerCase().startsWith("agent:")`, which is consistent with session key detection patterns used elsewhere in the codebase (`src/routing/session-key.ts`, `src/infra/state-migrations.ts`, `src/gateway/session-utils.ts`). - Placement is correct: after the message-required check but before the session resolution logic that would silently accept the malformed input. - No tests were added for this validation. While the logic is simple, a unit test covering the error case would strengthen confidence. <h3>Confidence Score: 4/5</h3> - This PR is safe to merge — it adds a straightforward input validation guard with no side effects on existing behavior. - The change is minimal (6 lines), isolated to an early validation check, and follows established codebase patterns for detecting session key formats. It only affects the error path for a specific misuse pattern and cannot regress normal operation. Deducting one point for the absence of a test covering the new error condition. - No files require special attention. _{Last reviewed commit: 78345e8} <!-- greptile_other_comments_section --> <!-- /greptile_comment -->