diff --git a/scripts/gen_schema.py b/scripts/gen_schema.py
index ad9c6fb..fc8d93d 100644
--- a/scripts/gen_schema.py
+++ b/scripts/gen_schema.py
@@ -120,6 +120,31 @@
     ),
 )
 
+# Classes that need a field_validator injected after generation.
+# Each entry: (class_name, field_name, validator_body)
+# The validator_body is the full method source (indented 4 spaces inside the class).
+CLASS_VALIDATOR_INJECTIONS: tuple[tuple[str, str, str], ...] = (
+    (
+        "InitializeRequest",
+        "protocol_version",
+        textwrap.dedent("""\
+            @field_validator("protocol_version", mode="before")
+            @classmethod
+            def _coerce_protocol_version(cls, v: Any) -> int:
+                # Some clients (e.g. Zed) send a date string like "2024-11-05" instead
+                # of an integer.  The Rust SDK treats any string as version 0; we map it
+                # to 1 (the current stable version) so the connection is not rejected.
+                # See: https://github.com/agentclientprotocol/rust-sdk/blob/main/crates/agent-client-protocol-schema/src/version.rs
+                if isinstance(v, int):
+                    return v
+                try:
+                    return int(v)
+                except (TypeError, ValueError):
+                    return 1
+        """),
+    ),
+)
+
 
 @dataclass(frozen=True)
 class _ProcessingStep:
@@ -182,6 +207,7 @@ def postprocess_generated_schema(output_path: Path) -> list[str]:
         _ProcessingStep("apply default overrides", _apply_default_overrides),
         _ProcessingStep("attach description comments", _add_description_comments),
         _ProcessingStep("ensure custom BaseModel", _ensure_custom_base_model),
+        _ProcessingStep("inject field validators", _inject_field_validators),
     )
 
     for step in processing_steps:
@@ -338,6 +364,51 @@ def __getattr__(self, item: str) -> Any:
     return "\n".join(lines) + "\n"
 
 
+def _ensure_pydantic_import(content: str, name: str) -> str:
+    """Add *name* to the ``from pydantic import ...`` line if not already present."""
+    lines = content.splitlines()
+    for idx, line in enumerate(lines):
+        if not line.startswith("from pydantic import "):
+            continue
+        imports = [part.strip() for part in line[len("from pydantic import "):].split(",")]
+        if name not in imports:
+            imports.append(name)
+            lines[idx] = "from pydantic import " + ", ".join(imports)
+        return "\n".join(lines) + "\n"
+    return content
+
+
+def _inject_field_validators(content: str) -> str:
+    """Inject field_validator methods into classes listed in CLASS_VALIDATOR_INJECTIONS."""
+    for class_name, _field_name, validator_body in CLASS_VALIDATOR_INJECTIONS:
+        # Ensure field_validator is imported from pydantic.
+        content = _ensure_pydantic_import(content, "field_validator")
+
+        # Find the end of the class body and append the validator before the next class.
+        class_pattern = re.compile(
+            rf"(class {class_name}\(BaseModel\):)(.*?)(?=\nclass |\Z)",
+            re.DOTALL,
+        )
+
+        def _append_validator(
+            match: re.Match[str],
+            _body: str = validator_body,
+            _class: str = class_name,
+        ) -> str:
+            header, block = match.group(1), match.group(2)
+            # Indent the validator body by 4 spaces to sit inside the class.
+            indented = "\n" + textwrap.indent(_body.rstrip(), "    ")
+            return header + block + indented + "\n"
+
+        content, count = class_pattern.subn(_append_validator, content, count=1)
+        if count == 0:
+            print(
+                f"Warning: class {class_name} not found for validator injection",
+                file=sys.stderr,
+            )
+    return content
+
+
 def _apply_field_overrides(content: str) -> str:
     for class_name, field_name, new_type, optional in FIELD_TYPE_OVERRIDES:
         if optional:
diff --git a/src/acp/schema.py b/src/acp/schema.py
index 32031c4..e8b9c54 100644
--- a/src/acp/schema.py
+++ b/src/acp/schema.py
@@ -6,7 +6,7 @@
 from enum import Enum
 from typing import Annotated, Any, Dict, List, Literal, Optional, Union
 
-from pydantic import BaseModel as _BaseModel, Field, RootModel, ConfigDict
+from pydantic import BaseModel as _BaseModel, Field, RootModel, ConfigDict, field_validator
 
 PermissionOptionKind = Literal["allow_once", "allow_always", "reject_once", "reject_always"]
 PlanEntryPriority = Literal["high", "medium", "low"]
@@ -1588,6 +1588,20 @@ class InitializeRequest(BaseModel):
         ),
     ]
 
+    @field_validator("protocol_version", mode="before")
+    @classmethod
+    def _coerce_protocol_version(cls, v: Any) -> int:
+        # Some clients (e.g. Zed) send a date string like "2024-11-05" instead
+        # of an integer.  The Rust SDK treats any string as version 0; we map it
+        # to 1 (the current stable version) so the connection is not rejected.
+        # See: https://github.com/agentclientprotocol/rust-sdk/blob/main/crates/agent-client-protocol-schema/src/version.rs
+        if isinstance(v, int):
+            return v
+        try:
+            return int(v)
+        except (TypeError, ValueError):
+            return 1
+
 
 class KillTerminalRequest(BaseModel):
     # The _meta property is reserved by ACP to allow clients and agents to attach additional