chore: import upstream snapshot with attribution

internal/platform/error.go

@@ -0,0 +1,56 @@
+// Copyright (c) 2026 Lark Technologies Pte. Ltd.
+// SPDX-License-Identifier: MIT
+
+package internalplatform
+
+import "fmt"
+
+// PluginInstallError is the typed install-time failure. ReasonCode comes
+// from the closed enum in the design doc (section 5.3 reason_code
+// table). Cause carries the underlying error, if any, so consumers can
+// errors.As to inspect it.
+type PluginInstallError struct {
+	PluginName string
+	ReasonCode string
+	Reason     string
+	Cause      error
+}
+
+func (e *PluginInstallError) Error() string {
+	prefix := fmt.Sprintf("plugin %q (%s)", e.PluginName, e.ReasonCode)
+	if e.Reason != "" {
+		prefix += ": " + e.Reason
+	}
+	if e.Cause != nil {
+		prefix += ": " + e.Cause.Error()
+	}
+	return prefix
+}
+
+func (e *PluginInstallError) Unwrap() error { return e.Cause }
+
+// ReasonCodes for PluginInstallError. The closed enum is referenced by
+// the design doc's hard-constraint #15 (reason_code enum closure) and
+// drives the JSON envelope's error.detail.reason_code field.
+const (
+	ReasonInvalidPluginName   = "invalid_plugin_name"
+	ReasonPluginNamePanic     = "plugin_name_panic"
+	ReasonInvalidHookName     = "invalid_hook_name"
+	ReasonDuplicateHookName   = "duplicate_hook_name"
+	ReasonInvalidHookRegister = "invalid_hook_registration"
+	ReasonInvalidRule         = "invalid_rule"
+	ReasonRestrictsMismatch   = "restricts_mismatch"
+	ReasonCapabilityUnmet     = "capability_unmet"
+	ReasonCapabilitiesPanic   = "capabilities_panic"
+	// ReasonInvalidCapability flags a plugin authoring error in
+	// Capabilities() output -- e.g. a syntactically malformed
+	// RequiredCLIVersion string. This is distinct from
+	// ReasonCapabilityUnmet (legitimate version mismatch): an authoring
+	// bug must NOT be hidden by FailurePolicy=FailOpen, so this code is
+	// classified as untrusted-config and aborts unconditionally.
+	ReasonInvalidCapability   = "invalid_capability"
+	ReasonInstallFailed       = "install_failed"
+	ReasonInstallPanic        = "install_panic"
+	ReasonDuplicatePluginName = "duplicate_plugin_name"
+	ReasonMultipleRestricts   = "multiple_restrict_plugins"
+)