feat: add list_files and grep_file skills tools

[brandonkeung]

Summary

• Adds native, in-process list_files and grep_file tools to both the Go (go/adk/pkg/skills, go/adk/pkg/tools) and Python (kagent-skills, kagent-adk) agent runtimes, alongside the existing read_file/write_file/edit_file/bash skills tools.
• Gives agents safe, non-privileged file visibility without depending on bash, which some deployments disable for privilege/security reasons.
• Hardened across several review passes; fixes along the way:
  • Go: a symlink-resolution inconsistency in resolveReadPath/resolveWritePath/resolveEditPath could reject valid paths under a symlinked session root.
  • Go: NewSkillsTools failed entirely (dropping all tools) when the bash command executor couldn't be constructed, instead of just omitting bash.
  • Go: filepath.WalkDir root resolution fixed so an unresolved symlink root is actually recursed into; an err-shadowing bug that silently truncated results on a WalkDir failure fixed.
  • Both: grep_file no longer hangs indefinitely on a FIFO (or other non-regular file) with no writer connected, in both the recursive walk and single-target paths.
  • Both: matched lines are capped to 2000 chars (matching read_file's existing convention) — previously unbounded in Python, and could fail the whole search past 1MB in Go.
  • Python: GrepFileTool now uses a dedicated thread pool instead of the shared default pool, since a hung regex match can't be forcibly killed and would otherwise starve unrelated work.
  • Both: a single unreadable file or subdirectory is now a skip rather than an abort of the whole search, so one bad entry doesn't discard matches already found elsewhere in the tree — annotated as "no matches found (N entries could not be read)" so a systemic failure isn't indistinguishable from a genuinely empty search.
  • Both: a fully unreadable search root now surfaces a real error instead of a misleadingly confident empty result.

Test plan

• Go: TestGrepContent (go/adk/pkg/skills/shell_test.go) — matches, recursion, symlink escape/resolution, FIFO hang safety, unreadable file/subdirectory/root handling, output truncation — and TestListFilesAndGrepFileTools_RunThroughADK, TestNewSkillsTools_OmitsBashWithoutSRTSettings (go/adk/pkg/tools/skills_test.go)
• Python: unit tests in kagent-skills/kagent-adk covering the same scenarios (path traversal, recursive/ignore-case, symlink escape, FIFO hang safety, unreadable file/subdirectory/root handling, truncation, GrepFileTool timeout behavior)
• All new regression tests verified to fail against the pre-fix code, confirming they exercise the actual bug
• Verified end-to-end in a live kind cluster via the browser UI for both runtimes (dedicated Go- and Python-runtime test agents), including the FIFO-hang scenario and the unreadable-subdirectory/root scenarios, each invoking list_files/grep_file by name and returning correct output

[Copilot]

Pull request overview

This PR extends Kagent’s agent toolsets (Go + Python runtimes) with native, in-process filesystem visibility tools—list_files and grep_file—so agents can inspect session/skills files without relying on bash (which may be disabled). It also adjusts Go path-resolution and tool construction behavior to be more robust around symlinked roots and missing sandbox-runtime settings.

Changes:

• Added list_files/grep_file tool descriptions and implementations for both Python (kagent-skills, kagent-adk) and Go (go/adk/pkg/skills, go/adk/pkg/tools).
• Updated Go tool initialization to omit bash when sandbox-runtime settings are unavailable, instead of failing the entire toolset.
• Added/expanded unit tests covering new directory listing and grep behaviors across both runtimes.

Reviewed changes

Copilot reviewed 12 out of 12 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
python/packages/kagent-skills/src/kagent/tests/unittests/test_skill_execution.py	Adds unit tests for list_dir_content / grep_content (including traversal/recursive/error cases).
python/packages/kagent-skills/src/kagent/skills/shell.py	Implements list_dir_content and grep_content core logic.
python/packages/kagent-skills/src/kagent/skills/prompts.py	Adds standardized prompt/description text for list_files and grep_file.
python/packages/kagent-skills/src/kagent/skills/init.py	Exposes new functions/descriptions in the public skills package API.
python/packages/kagent-adk/src/kagent/adk/tools/skills_toolset.py	Adds ListFilesTool/GrepFileTool to the default ADK toolset.
python/packages/kagent-adk/src/kagent/adk/tools/skills_plugin.py	Ensures agents get list_files / grep_file tools when missing.
python/packages/kagent-adk/src/kagent/adk/tools/file_tools.py	Introduces ADK tool wrappers ListFilesTool and GrepFileTool wired to skills implementations.
python/packages/kagent-adk/src/kagent/adk/tools/init.py	Exports the new tool classes.
go/adk/pkg/tools/skills.go	Adds Go list_files/grep_file, makes bash optional, and adjusts symlink root resolution.
go/adk/pkg/tools/skills_test.go	Adds tests for toolset composition and end-to-end tool invocation via functiontool.Run().
go/adk/pkg/skills/shell.go	Adds Go implementations ListDirContent and GrepContent.
go/adk/pkg/skills/shell_test.go	Adds unit tests for the new Go directory listing and grep functions.

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