fix: stop repeated tool-call loops - #2651

Related Issue

Resolve #2637

Description

This PR turns the repeated identical tool-call guard into a hard stop before executing another duplicate call once the repeat limit is reached.

Previously, the runtime set the stop flag at the limit but still executed that final repeated call and only stopped the turn afterward. Now the toolset returns a repeat-limit error immediately at the stop threshold, so the agent loop can end the turn without performing one more identical Read call. The existing repeated-call reminder behavior before the hard stop is preserved.

Verification

• Verified the focused before/after behavior locally: the previous implementation executed the twelfth identical call, while the updated implementation stops before that call and returns the repeat-limit result.
• Verified the changed files compile.
• The targeted repository test command could not run in this offline worktree because the test runner is not installed and dependency installation was intentionally skipped; project online checks can run the full suite.

Checklist

• I have read the CONTRIBUTING document.
• I have linked the related issue, if any.
• I have added tests that prove my fix is effective or that my feature works.
• I have run make gen-changelog to update the changelog. Not needed for this internal runtime bug fix.
• I have run make gen-docs to update the user documentation. Not needed for this internal runtime bug fix.