#18647: fix(agents): guard against undefined paths in injectedFiles

## Summary - Filter `injectedFiles` to exclude entries with `undefined` or empty `path` before iterating in `buildInjectedWorkspaceFiles`, preventing a `TypeError: Cannot read properties of undefined (reading 'replace')` crash - Matches the existing guard pattern already applied in `system-prompt.ts` (`validContextFiles` filter at line 603) - Adds regression test verifying the function handles `undefined` and empty paths without crashing ## Root Cause When workspace bootstrap files exceed `bootstrapMaxChars`, the bootstrap context builder can produce `EmbeddedContextFile` entries where `path` is `undefined`. The `buildInjectedWorkspaceFiles` function in `system-prompt-report.ts` calls `file.path.replace(/\\/g, "/")` without checking for this, causing a TypeError that crashes **all agents** before any API call. The same guard was already added to `buildAgentSystemPrompt` in `system-prompt.ts` (the `validContextFiles` filter), but was missing from the report builder. ## Test plan - [x] Added test: `does not crash when injectedFiles contain entries with undefined path` - [x] All 5 tests in `system-prompt-report.test.ts` pass - [x] Verified fix resolves the crash on a live gateway (v2026.2.15) with Gemini agents Fixes #17947 <!-- greptile_comment --> <h3>Greptile Summary</h3> Adds a defensive filter in `buildInjectedWorkspaceFiles` (`system-prompt-report.ts`) to exclude `EmbeddedContextFile` entries with `undefined` or empty `path` before iterating. This prevents a `TypeError` crash when `file.path.replace(/\\\\/g, "/")` is called on an undefined path — a scenario that occurs when workspace bootstrap files exceed `bootstrapMaxChars`. - Mirrors the existing `validContextFiles` guard already present in `system-prompt.ts:603` - Includes a regression test covering both `undefined` and empty-string path cases - Minimal, focused change that addresses a real production crash <h3>Confidence Score: 5/5</h3> - This PR is safe to merge — it adds a defensive filter that prevents a runtime crash without changing any existing behavior for valid inputs. - The change is minimal, well-scoped, and follows an established pattern already used elsewhere in the codebase (system-prompt.ts:603). It only filters out invalid entries that would cause a TypeError, and includes a regression test. No risk of breaking existing functionality. - No files require special attention. _{Last reviewed commit: 8ea6a4e} <!-- greptile_other_comments_section --> _{(2/5) Greptile learns from your feedback when you react with thumbs up/down!} <!-- /greptile_comment -->