fix(web): don't include sources in grep tool when groupByRepo=true

[brendan-kellam]

Summary

• When groupByRepo=true, the grep tool was still including all matched files as sources in the tool result, even though the LLM only receives a repo-level summary and never references individual files
• This caused 1000+ individual setSources() state updates to be dispatched to the client, each triggering a full re-render of the chat thread and all message pairs
• Fix: omit sources from the return value when groupByRepo=true

Test plan

• Run a search that uses groupByRepo=true and confirm the UI no longer freezes when results return
• Confirm the hover card in the grep tool component still shows repo-grouped results correctly
• Run a normal (non-grouped) grep and confirm file sources still appear as expected

Fixes SOU-730

🤖 Generated with Claude Code

Summary by CodeRabbit

• Bug Fixes
  • Resolved UI freeze that occurred when the grep tool returned large result sets with group-by-repository enabled.

[coderabbitai]

Walkthrough

The pull request fixes a UI freeze issue that occurred when the grep tool returned large result sets with groupByRepo enabled. The fix restructures when the sources field is constructed in the grep execution logic, deferring its creation in the grouped-by-repo path.

Changes

Cohort / File(s)	Summary
Documentation CHANGELOG.md	Added entry documenting resolution of UI freeze when grep returns large result sets with groupByRepo=true.
Grep Tool Execution packages/web/src/features/tools/grep.ts	Modified grepDefinition.execute to defer sources construction: returns undefined when groupByRepo=true, and constructs sources after output/truncation handling only in the non-grouped path.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~12 minutes

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately summarizes the main change: preventing the grep tool from including sources when groupByRepo=true, which directly addresses the UI freeze bug documented in the PR objectives.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.

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✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch brendan-kellam/fix-grep-groupbyrepo-sources-SOU-730

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