issue intents: align rationale maxLength to API limit of 280 characters

[alondahari]

Summary

The rationale field on set_issue_type, set_issue_field, and add_labels has no maxLength in the tool schema (safe_outputs_tools.json), so the agent writes arbitrarily long rationales. The runtime truncates to 1024 characters (issue_intents.cjs), but the GitHub API enforces a 280 character limit — causing mutations to fail with "rationale is too long (maximum is 280)".

Root cause

Three layers with mismatched limits:

Layer	Limit	Effect
Tool schema (safe_outputs_tools.json)	none	Agent writes unbounded rationales
Runtime validation (issue_intents.cjs)	1024	Truncates, but still too long for API
GitHub GraphQL API	280	Rejects anything over 280 chars

Fix

1. safe_outputs_tools.json — Add maxLength: 280 and update description to "Optional rationale for the change (max 280 characters)." on all rationale fields:

   • set_issue_type.rationale
   • set_issue_field.rationale
   • add_labels.labels[].rationale
   • remove_labels.labels[].rationale
   • update_issue.labels[].rationale

2. issue_intents.cjs — Change ISSUE_INTENT_RATIONALE_MAX_LENGTH from 1024 to 280.

3. safe_output_type_validator.cjs — Change hardcoded maxLength: 1024 to 280 in the label rationale sanitization (line 136).

4. safe_output_type_validator.test.cjs — Update test expectations from 1024 to 280.

Affected files

• actions/setup/js/safe_outputs_tools.json
• actions/setup/js/issue_intents.cjs
• actions/setup/js/safe_output_type_validator.cjs
• actions/setup/js/safe_output_type_validator.test.cjs

Verification

Validated locally — all 86 validator tests and 65 add_labels/set_issue_field tests pass after the change.

The 280 limit was confirmed by a live workflow run in a sandbox where a rationale exceeding 280 chars caused:

Failed to set issue field on issue #551: Request failed due to following response errors:
 - rationale is too long (maximum is 280)