## Summary
Enhances the `init_chat_model` function with comprehensive input
validation, improved model inference patterns, and better error handling
to provide a significantly improved user experience.
## Changes Made
- ✅ **Input Validation**: Added comprehensive type and value checking
for all parameters
- ✅ **Enhanced Model Inference**: Improved pattern matching with
case-insensitive support and new model patterns
- ✅ **Better Error Messages**: Detailed error messages with examples and
documentation links
- ✅ **Comprehensive Tests**: Added extensive test coverage for all new
functionality
- ✅ **Documentation**: Enhanced docstrings and examples
## Backward Compatibility
All changes are fully backward compatible. No breaking changes
introduced.
## Testing
- Added 6 new test functions covering input validation, model inference,
and error handling
- All existing tests continue to pass
- Comprehensive parametrized testing for various model patterns
## User Experience Improvements
- Better error messages help users quickly resolve configuration issues
- Enhanced model inference reduces the need to specify providers
explicitly
- Comprehensive input validation catches issues early with helpful
guidance
---------
Co-authored-by: Mason Daugherty <github@mdrxy.com>
Co-authored-by: Mason Daugherty <mason@langchain.dev>
If the `stdout` "done marker" arrives before the `stderr` output is
enqueued, the method returns early without capturing the `stderr` line.
The two reader threads run independently with no synchronization
guaranteeing `stderr` arrives before the done marker.
In environments with Python 3.10, timing differences can cause the
`stdout` marker to win the race, resulting in `<no output>` instead of
`[stderr]` error.
Observed as a flaky test on `test_stderr_output_labeling` in CI:
```shell
FAILED tests/unit_tests/agents/middleware/implementations/test_shell_tool.py::test_stderr_output_labeling - AssertionError: assert '[stderr] error' in '<no output>'
```
Use of the fixture `_base_vcr_config` is deprecated with alternative
function `base_vcr_config()`
This way:
* we don't need to import `_base_vcr_config` seen as unused (which leads
to ruff violations PLC0414 and F811)
* we don't need to make a copy since a new dict is created at each
function invocation
Co-authored-by: Mason Daugherty <mason@langchain.dev>
With this we get the correct types for `_runnable_support` annotated
functions.
* return list[BaseMessage] when messages is not None
* return Runnable when messages is None
* typing of function args
This PR changes how we find the cutoff for summarization, summarizing
content more eagerly if the initial cutoff point isn't safe (ie, would
break apart AI + tool message pairs)
This new algorithm is quite simple - it looks at the initial cutoff
point, if it's not safe, moves forward through the message list until it
finds the first non tool message.
For example:
```
H
AI
TM
--- theoretical cutoff based keep=('messages', 3)
TM
AI
TM
```
```
H
AI
TM
TM
--- actual cutoff, more aggressive summarization
AI
TM
```
The `HumanInTheLoopMiddleware` is missing a type annotation for the
context schema. Without the fix in this PR, the following code does not
type check:
```
graph = create_agent(
"gpt-5",
tools=[send_email_tool, read_email_tool],
middleware=[
HumanInTheLoopMiddleware(
interrupt_on={
# Require approval or rejection for sending emails
"send_email_tool": {
"allowed_decisions": ["approve", "reject"],
},
# Auto-approve reading emails
"read_email_tool": False,
}
),
],
context_schema=ContextSchema,
)
```
```
Argument of type "list[HumanInTheLoopMiddleware]" cannot be assigned to parameter "middleware" of type "Sequence[AgentMiddleware[StateT_co@create_agent, ContextT@create_agent]]" in function "create_agent"
"HumanInTheLoopMiddleware" is not assignable to "AgentMiddleware[AgentState[Unknown], ContextSchema | None]"
Type parameter "ContextT@AgentMiddleware" is invariant, but "None" is not the same as "ContextSchema | None"
```
* `create_agent`'s `system_prompt` allows `str | SystemMessage`
* added `system_message: SystemMessage` on `ModelRequest`
* `ModelRequest.system_prompt` is a function of `system_message.text`,
now deprecated
* disallow setting `system_prompt` and `system_message`
* `ModelRequest.system_prompt` can still be set (w/ custom setattr) for
custom backwards compat, but the updates just get propogated to the
`ModelRequest.system_message`
---------
Co-authored-by: Chester Curme <chester.curme@gmail.com>
Closes https://github.com/langchain-ai/langchain/issues/33983
* Adds `ModelRetryMiddleware` modeled after `ToolRetryMiddleware`
* Uses `on_failure` modes of `error` and `continue` to match the
`exit_behavior` modes of model + tool call limit middleware
* In a backwards compatible manner, aligns the API of
`ToolRetryMiddleware`'s `on_failure` with the above
* Centralize common "retry" utils across these middlewares
