fix(tools): avoid panic in StripToolPrefix on overlapping prefix+suffix (#1398)

When a tool_call_prefix template has both a prefix and a suffix
(e.g. "pre_{tool_name}_suf"), StripToolPrefix stripped the prefix and
then sliced off the suffix length without checking the two ends don't
overlap. A model-emitted name that satisfies both HasPrefix and
HasSuffix but is shorter than prefix+suffix (e.g. "pre_suf") produced a
negative slice length -> "slice bounds out of range [:-1]" panic. This
runs in the agent turn loop on LLM-controlled names
(resolveToolCallName -> StripToolPrefix), so a crafted/degenerate name
crashes the turn.

Guard with len(prefix)+len(suffix) <= len(name); overlapping names now
fall through to returning the name unchanged, consistent with the other
no-match fallbacks. Adds a regression row to the prefix test table.

internal/tools/policy.go

@@ -527,7 +527,11 @@ func StripToolPrefix(tmpl, name string) string {
 	if strings.Contains(tmpl, placeholder) {
 		parts := strings.SplitN(tmpl, placeholder, 2)
 		prefix, suffix := parts[0], parts[1]
-		if strings.HasPrefix(name, prefix) && strings.HasSuffix(name, suffix) {
+		// Require the name to be at least as long as prefix+suffix so an
+		// overlapping match (e.g. tmpl "pre_{tool_name}_suf", name "pre_suf")
+		// doesn't slice with a negative length and panic.
+		if strings.HasPrefix(name, prefix) && strings.HasSuffix(name, suffix) &&
+			len(prefix)+len(suffix) <= len(name) {
 			result := name[len(prefix):]
 			if suffix != "" {
 				result = result[:len(result)-len(suffix)]

internal/tools/policy_prefix_test.go

@@ -16,6 +16,7 @@ func TestStripToolPrefix(t *testing.T) {
 		{"template no match", "proxy_{tool_name}", "other_exec", "other_exec"},
 		{"template empty result", "proxy_{tool_name}", "proxy_", "proxy_"},
 		{"template exact placeholder", "{tool_name}", "exec", "exec"},
+		{"template prefix+suffix overlap (regression)", "pre_{tool_name}_suf", "pre_suf", "pre_suf"},
 
 		// Literal prefix
 		{"literal prefix with separator", "proxy_", "proxy_exec", "exec"},