fix(types): address Greptile review feedback

Three issues from Greptile's review (4/5 confidence, all P1/P2):

1. Back-compat shim at `agentex.lib.types.acp` was missing two public
   names from the original module: `RPC_SYNC_METHODS` and
   `PARAMS_MODEL_BY_METHOD`. External consumers importing those from the
   old path would have hit ImportError, breaking the PR's "zero install-
   time impact" guarantee. Added both to the re-export list.

2. `agentex.protocol.json_rpc` silently dropped `from_attributes=True`
   and `populate_by_name=True` config when switching from
   `model_utils.BaseModel` to plain `pydantic.BaseModel`. Restored via
   an explicit `model_config = ConfigDict(...)` on all three classes,
   with a comment explaining why. The previous version inherited these
   flags transitively; making them explicit + documented avoids drift.

3. All 10 CLI scaffolding templates (`agentex init`) generated
   `from agentex.lib.types.acp import ...` — works via the shim but
   immediately stale on the day this PR establishes
   `agentex.protocol.acp` as canonical. Updated all templates to use
   the new path so scaffolded code starts on the right foot.

Verified locally:
- ruff check . → All checks passed
- shim re-exports all 7 original symbols (5 classes + 2 module-level
  constants), identity-checked vs canonical
- JSONRPCRequest/Response/Error all have
  `model_config.get('from_attributes') is True` and
  `populate_by_name is True`

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: max-parke-scale

src/agentex/lib/cli/templates/default-langgraph/project/acp.py.j2

@@ -18,7 +18,7 @@ import agentex.lib.adk as adk
 from agentex.lib.adk import create_langgraph_tracing_handler, stream_langgraph_events
 from agentex.lib.core.tracing.tracing_processor_manager import add_tracing_processor_config
 from agentex.lib.sdk.fastacp.fastacp import FastACP
-from agentex.lib.types.acp import SendEventParams, CancelTaskParams, CreateTaskParams
+from agentex.protocol.acp import SendEventParams, CancelTaskParams, CreateTaskParams
 from agentex.lib.types.fastacp import AsyncACPConfig
 from agentex.lib.types.tracing import SGPTracingProcessorConfig
 from agentex.lib.utils.logging import make_logger

src/agentex/lib/cli/templates/default-pydantic-ai/project/acp.py.j2

@@ -28,7 +28,7 @@ from agentex.lib.adk import (
     stream_pydantic_ai_events,
     create_pydantic_ai_tracing_handler,
 )
-from agentex.lib.types.acp import SendEventParams, CancelTaskParams, CreateTaskParams
+from agentex.protocol.acp import SendEventParams, CancelTaskParams, CreateTaskParams
 from agentex.lib.types.fastacp import AsyncACPConfig
 from agentex.lib.types.tracing import SGPTracingProcessorConfig
 from agentex.lib.utils.logging import make_logger

src/agentex/lib/cli/templates/default/project/acp.py.j2

@@ -1,6 +1,6 @@
 from agentex.lib.sdk.fastacp.fastacp import FastACP
 from agentex.lib.types.fastacp import AsyncACPConfig
-from agentex.lib.types.acp import SendEventParams, CancelTaskParams, CreateTaskParams
+from agentex.protocol.acp import SendEventParams, CancelTaskParams, CreateTaskParams
 from agentex.lib.utils.logging import make_logger
 from agentex.types.text_content import TextContent
 from agentex.lib import adk

src/agentex/lib/cli/templates/sync-langgraph/project/acp.py.j2

@@ -11,7 +11,7 @@ import agentex.lib.adk as adk
 from agentex.lib.adk import create_langgraph_tracing_handler, convert_langgraph_to_agentex_events
 from agentex.lib.core.tracing.tracing_processor_manager import add_tracing_processor_config
 from agentex.lib.sdk.fastacp.fastacp import FastACP
-from agentex.lib.types.acp import SendMessageParams
+from agentex.protocol.acp import SendMessageParams
 from agentex.lib.types.tracing import SGPTracingProcessorConfig
 from agentex.lib.utils.logging import make_logger
 from agentex.types.task_message_content import TaskMessageContent

src/agentex/lib/cli/templates/sync-openai-agents/project/acp.py.j2

@@ -4,7 +4,7 @@ from typing import AsyncGenerator, List
 from agentex.lib import adk
 from agentex.lib.adk.providers._modules.sync_provider import SyncStreamingProvider, convert_openai_to_agentex_events
 from agentex.lib.sdk.fastacp.fastacp import FastACP
-from agentex.lib.types.acp import SendMessageParams
+from agentex.protocol.acp import SendMessageParams
 from agentex.lib.core.tracing.tracing_processor_manager import add_tracing_processor_config
 from agentex.lib.types.tracing import SGPTracingProcessorConfig
 from agentex.lib.utils.model_utils import BaseModel

src/agentex/lib/cli/templates/sync-pydantic-ai/project/acp.py.j2

@@ -22,7 +22,7 @@ from agentex.lib.adk import (
     create_pydantic_ai_tracing_handler,
     convert_pydantic_ai_to_agentex_events,
 )
-from agentex.lib.types.acp import SendMessageParams
+from agentex.protocol.acp import SendMessageParams
 from agentex.lib.types.tracing import SGPTracingProcessorConfig
 from agentex.lib.utils.logging import make_logger
 from agentex.lib.sdk.fastacp.fastacp import FastACP

src/agentex/lib/cli/templates/sync/project/acp.py.j2

@@ -1,6 +1,6 @@
 from typing import AsyncGenerator, Union
 from agentex.lib.sdk.fastacp.fastacp import FastACP
-from agentex.lib.types.acp import SendMessageParams
+from agentex.protocol.acp import SendMessageParams
 
 from agentex.types.task_message_update import TaskMessageUpdate
 from agentex.types.task_message_content import TaskMessageContent

src/agentex/lib/cli/templates/temporal-openai-agents/project/workflow.py.j2

@@ -4,7 +4,7 @@ import os
 from temporalio import workflow
 
 from agentex.lib import adk
-from agentex.lib.types.acp import CreateTaskParams, SendEventParams
+from agentex.protocol.acp import CreateTaskParams, SendEventParams
 from agentex.lib.core.temporal.workflows.workflow import BaseWorkflow
 from agentex.lib.core.temporal.types.workflow import SignalName
 from agentex.lib.utils.logging import make_logger

src/agentex/lib/cli/templates/temporal-pydantic-ai/project/workflow.py.j2

@@ -23,7 +23,7 @@ from temporalio import workflow
 from project.agent import TaskDeps, temporal_agent
 
 from agentex.lib import adk
-from agentex.lib.types.acp import SendEventParams, CreateTaskParams
+from agentex.protocol.acp import SendEventParams, CreateTaskParams
 from agentex.lib.types.tracing import SGPTracingProcessorConfig
 from agentex.lib.utils.logging import make_logger
 from agentex.types.text_content import TextContent

src/agentex/lib/cli/templates/temporal/project/workflow.py.j2

@@ -3,7 +3,7 @@ import json
 from temporalio import workflow
 
 from agentex.lib import adk
-from agentex.lib.types.acp import CreateTaskParams, SendEventParams
+from agentex.protocol.acp import CreateTaskParams, SendEventParams
 from agentex.lib.core.temporal.workflows.workflow import BaseWorkflow
 from agentex.lib.core.temporal.types.workflow import SignalName
 from agentex.lib.utils.logging import make_logger