#15162: Include tool args in verbose preview summaries

## Summary - Include primary tool args (path/filename/target/etc.) in verbose preview summaries. - Improves real‑time visibility of *where* tools are acting (e.g., `read: src/app.ts`). - Adds a unit test to cover path inclusion. ## Changes - Add `extractToolSummaries()` to build `tool: arg` summaries. - Prefer `path/file_path/filePath/filename`, fallback to `target/url/query/command`. - Update preview builder to use summaries. - Add test: “includes tool path in preview summary when available”. ## Notes - Does not alter tool execution—only summary formatting. - Falls back gracefully when args are missing. <!-- greptile_comment --> <h2>Greptile Overview</h2> <h3>Greptile Summary</h3> This PR changes the session preview builder to include a primary tool argument in the verbose preview text (e.g., `call read: src/app.ts`) by adding `extractToolSummaries()` and switching the preview fallback from tool names to these summaries. It also adds a unit test intended to cover path inclusion. The main issue is in the new test: it writes the transcript using a broken join delimiter (`lines.join("<newline>")` as a multi-line string literal) and the next test starts immediately after the previous block without proper separation, both of which are likely to fail formatting/parsing and CI checks. <h3>Confidence Score: 3/5</h3> - Not safe to merge as-is due to a broken unit test change. - The preview summary logic change is localized and reasonably defensive, but the new test introduces an invalid join delimiter / formatting issues that will likely fail parsing or formatting checks in CI until corrected. - src/gateway/session-utils.fs.test.ts _{Last reviewed commit: 9788ace} <!-- greptile_other_comments_section --> _{(2/5) Greptile learns from your feedback when you react with thumbs up/down!} <!-- /greptile_comment -->