Add agent library

Signed-off-by: Bryan Frimin <bryan@getprobo.com>

pkg/agent/errors.go

@@ -0,0 +1,71 @@
+// Copyright (c) 2026 Probo Inc <hello@getprobo.com>.
+//
+// Permission to use, copy, modify, and/or distribute this software for any
+// purpose with or without fee is hereby granted, provided that the above
+// copyright notice and this permission notice appear in all copies.
+//
+// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
+// REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
+// AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
+// INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
+// LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
+// OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
+// PERFORMANCE OF THIS SOFTWARE.
+
+package agent
+
+import (
+	"fmt"
+
+	"go.probo.inc/probo/pkg/llm"
+)
+
+type (
+	MaxTurnsExceededError struct {
+		MaxTurns int
+	}
+
+	InputGuardrailTrippedError struct {
+		Guardrail string
+		Message   string
+	}
+
+	OutputGuardrailTrippedError struct {
+		Guardrail string
+		Message   string
+	}
+
+	InterruptedError struct {
+		ToolCalls        []llm.ToolCall
+		PendingApprovals []llm.ToolCall
+		Agent            *Agent
+		Messages         []llm.Message
+		Usage            llm.Usage
+		Turns            int
+	}
+
+	needsApprovalError struct {
+		allToolCalls     []llm.ToolCall
+		pendingApprovals []llm.ToolCall
+	}
+)
+
+func (e *MaxTurnsExceededError) Error() string {
+	return fmt.Sprintf("agent exceeded maximum number of turns (%d)", e.MaxTurns)
+}
+
+func (e *InputGuardrailTrippedError) Error() string {
+	return fmt.Sprintf("input guardrail %q tripped: %s", e.Guardrail, e.Message)
+}
+
+func (e *OutputGuardrailTrippedError) Error() string {
+	return fmt.Sprintf("output guardrail %q tripped: %s", e.Guardrail, e.Message)
+}
+
+func (e *InterruptedError) Error() string {
+	return fmt.Sprintf("run interrupted: %d tool call(s) require approval", len(e.PendingApprovals))
+}
+
+func (e *needsApprovalError) Error() string {
+	return fmt.Sprintf("%d tool call(s) require approval", len(e.pendingApprovals))
+}