[dotnet-port-fixes] Revalidate file skill paths before use

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The original pull request description is below.

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Summary

• Revalidate discovered file-skill resource and script paths against the original discovery root immediately before reading or running them.
• Preserve the existing file-backed skill API and runner metadata while rejecting parent-directory or skill-directory symlink swaps after discovery.
• Add regression tests covering resource reads and script runs after a discovered parent path is replaced with a symlink.

Ported .NET PRs

• .NET: fix: revalidate file skill paths before use agent-framework#8151 - revalidate file-backed skill resource and script paths before use
  • Upstream commit: 5b188dd80e46d6fe7ae57ca88c4a51bb2e10021b

Breaking Changes

No. The Go public API is unchanged; discovered file-backed skills now fail safely if their underlying path is replaced by a symlink after discovery.

Tests and Examples

• go test ./agent/skills/fsskills ./agent/skills
• Added regression tests for resource reads and script runs after parent-directory symlink replacement
• No example changes

Notes

• I classified this as a fixes port because the upstream diff only added internal path-scope and validation helpers plus resource/script call-site checks; it did not add public options, builders, or exported contract changes.
• Recent upstream work such as the session-store promotion and OpenTelemetry source-name changes was deferred because it changes public API or targets .NET-only surfaces.

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Show patch preview (62 of 329 lines)

From a58c9e2588a88c6b03fd3aab937aaddc19f49aa4 Mon Sep 17 00:00:00 2001
X-GH-AW-Base-Commit: 4b46045b01079041f0b8f5121b4cf66a79be8bd3
From: "github-actions[bot]" <github-actions[bot]@users.noreply.github.com>
Date: Wed, 16 Sep 2026 02:48:21 +0000
Subject: [PATCH] [dotnet-port-fixes] Revalidate file skill paths before use

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
---
 agent/skills/fsskills/path_scope.go         | 92 +++++++++++++++++++++
 agent/skills/fsskills/source.go             | 39 +++++----
 agent/skills/fsskills/source_script_test.go | 35 ++++++++
 agent/skills/fsskills/source_test.go        | 25 ++++++
 4 files changed, 177 insertions(+), 14 deletions(-)
 create mode 100644 agent/skills/fsskills/path_scope.go

diff --git a/agent/skills/fsskills/path_scope.go b/agent/skills/fsskills/path_scope.go
new file mode 100644
index 0000000..20ecbea
--- /dev/null
+++ b/agent/skills/fsskills/path_scope.go
@@ -0,0 +1,92 @@
+// Copyright (c) Microsoft. All rights reserved.
+
+package fsskills
+
+import (
+	"errors"
+	"fmt"
+	"io/fs"
+	"path"
+	"strings"
+)
+
+type skillPathScope struct {
+	rootFS         fs.FS
+	skillDirPath   string
+	skillDirPrefix string
+}
+
+func newSkillPathScope(rootFS fs.FS, skillDirPath string) skillPathScope {
+	skillDirPath = path.Clean(skillDirPath)
+	skillDirPrefix := ""
+	if skillDirPath != "." {
+		skillDirPrefix = skillDirPath + "/"
+	}
+	return skillPathScope{
+		rootFS:         rootFS,
+		skillDirPath:   skillDirPath,
+		skillDirPrefix: skillDirPrefix,
+	}
+}
+
+func (s skillPathScope) validateDiscoveredPathForUse(relativePath, kind string) (string, error) {
+	fullPath := path.Clean(relativePath)
+	if s.skillDirPath != "." {
+		fullPath = path.Clean(path.Join(s.skillDirPath, relativePath))
+	}
+	if !s.contains(fullPath) {
+		return "", fmt.Errorf("%s file %q references a path outside the skill directory", kind, relativePath)
+	}
+	if hasLinkOrInspectionFailureInPath(s.rootFS, fullPath) {
+		return "", fmt.Errorf
... (truncated)

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Generated by .NET to Go Fixes and Test Porting Agent · copilot · gpt54 · 210.3 AIC · ⌖ 10.7 AIC · ⊞ 19K · ◷

[michelle-clayton-work]

Pull request #1089 is linked to this issue and will close it when merged.