feat: split API and provider specs into separate llama-stack-api pkg (#3895)

# What does this PR do?

Extract API definitions and provider specifications into a standalone
llama-stack-api package that can be published to PyPI independently of
the main llama-stack server.


see: https://github.com/llamastack/llama-stack/pull/2978 and
https://github.com/llamastack/llama-stack/pull/2978#issuecomment-3145115942

Motivation

External providers currently import from llama-stack, which overrides
the installed version and causes dependency conflicts. This separation
allows external providers to:

- Install only the type definitions they need without server
dependencies
- Avoid version conflicts with the installed llama-stack package
- Be versioned and released independently

This enables us to re-enable external provider module tests that were
previously blocked by these import conflicts.

Changes

- Created llama-stack-api package with minimal dependencies (pydantic,
jsonschema)
- Moved APIs, providers datatypes, strong_typing, and schema_utils
- Updated all imports from llama_stack.* to llama_stack_api.*
- Configured local editable install for development workflow
- Updated linting and type-checking configuration for both packages

Next Steps

- Publish llama-stack-api to PyPI
- Update external provider dependencies
- Re-enable external provider module tests


Pre-cursor PRs to this one:

- #4093 
- #3954 
- #4064 

These PRs moved key pieces _out_ of the Api pkg, limiting the scope of
change here.


relates to #3237 

## Test Plan

Package builds successfully and can be imported independently. All
pre-commit hooks pass with expected exclusions maintained.

---------

Signed-off-by: Charlie Doern <cdoern@redhat.com>

src/llama-stack-api/llama_stack_api/prompts.py

@@ -0,0 +1,204 @@
+# Copyright (c) Meta Platforms, Inc. and affiliates.
+# All rights reserved.
+#
+# This source code is licensed under the terms described in the LICENSE file in
+# the root directory of this source tree.
+
+import re
+import secrets
+from typing import Protocol, runtime_checkable
+
+from pydantic import BaseModel, Field, field_validator, model_validator
+
+from llama_stack_api.common.tracing import telemetry_traceable
+from llama_stack_api.schema_utils import json_schema_type, webmethod
+from llama_stack_api.version import LLAMA_STACK_API_V1
+
+
+@json_schema_type
+class Prompt(BaseModel):
+    """A prompt resource representing a stored OpenAI Compatible prompt template in Llama Stack.
+
+    :param prompt: The system prompt text with variable placeholders. Variables are only supported when using the Responses API.
+    :param version: Version (integer starting at 1, incremented on save)
+    :param prompt_id: Unique identifier formatted as 'pmpt_<48-digit-hash>'
+    :param variables: List of prompt variable names that can be used in the prompt template
+    :param is_default: Boolean indicating whether this version is the default version for this prompt
+    """
+
+    prompt: str | None = Field(default=None, description="The system prompt with variable placeholders")
+    version: int = Field(description="Version (integer starting at 1, incremented on save)", ge=1)
+    prompt_id: str = Field(description="Unique identifier in format 'pmpt_<48-digit-hash>'")
+    variables: list[str] = Field(
+        default_factory=list, description="List of variable names that can be used in the prompt template"
+    )
+    is_default: bool = Field(
+        default=False, description="Boolean indicating whether this version is the default version"
+    )
+
+    @field_validator("prompt_id")
+    @classmethod
+    def validate_prompt_id(cls, prompt_id: str) -> str:
+        if not isinstance(prompt_id, str):
+            raise TypeError("prompt_id must be a string in format 'pmpt_<48-digit-hash>'")
+
+        if not prompt_id.startswith("pmpt_"):
+            raise ValueError("prompt_id must start with 'pmpt_' prefix")
+
+        hex_part = prompt_id[5:]
+        if len(hex_part) != 48:
+            raise ValueError("prompt_id must be in format 'pmpt_<48-digit-hash>' (48 lowercase hex chars)")
+
+        for char in hex_part:
+            if char not in "0123456789abcdef":
+                raise ValueError("prompt_id hex part must contain only lowercase hex characters [0-9a-f]")
+
+        return prompt_id
+
+    @field_validator("version")
+    @classmethod
+    def validate_version(cls, prompt_version: int) -> int:
+        if prompt_version < 1:
+            raise ValueError("version must be >= 1")
+        return prompt_version
+
+    @model_validator(mode="after")
+    def validate_prompt_variables(self):
+        """Validate that all variables used in the prompt are declared in the variables list."""
+        if not self.prompt:
+            return self
+
+        prompt_variables = set(re.findall(r"{{\s*(\w+)\s*}}", self.prompt))
+        declared_variables = set(self.variables)
+
+        undeclared = prompt_variables - declared_variables
+        if undeclared:
+            raise ValueError(f"Prompt contains undeclared variables: {sorted(undeclared)}")
+
+        return self
+
+    @classmethod
+    def generate_prompt_id(cls) -> str:
+        # Generate 48 hex characters (24 bytes)
+        random_bytes = secrets.token_bytes(24)
+        hex_string = random_bytes.hex()
+        return f"pmpt_{hex_string}"
+
+
+class ListPromptsResponse(BaseModel):
+    """Response model to list prompts."""
+
+    data: list[Prompt]
+
+
+@runtime_checkable
+@telemetry_traceable
+class Prompts(Protocol):
+    """Prompts
+
+    Protocol for prompt management operations."""
+
+    @webmethod(route="/prompts", method="GET", level=LLAMA_STACK_API_V1)
+    async def list_prompts(self) -> ListPromptsResponse:
+        """List all prompts.
+
+        :returns: A ListPromptsResponse containing all prompts.
+        """
+        ...
+
+    @webmethod(route="/prompts/{prompt_id}/versions", method="GET", level=LLAMA_STACK_API_V1)
+    async def list_prompt_versions(
+        self,
+        prompt_id: str,
+    ) -> ListPromptsResponse:
+        """List prompt versions.
+
+        List all versions of a specific prompt.
+
+        :param prompt_id: The identifier of the prompt to list versions for.
+        :returns: A ListPromptsResponse containing all versions of the prompt.
+        """
+        ...
+
+    @webmethod(route="/prompts/{prompt_id}", method="GET", level=LLAMA_STACK_API_V1)
+    async def get_prompt(
+        self,
+        prompt_id: str,
+        version: int | None = None,
+    ) -> Prompt:
+        """Get prompt.
+
+        Get a prompt by its identifier and optional version.
+
+        :param prompt_id: The identifier of the prompt to get.
+        :param version: The version of the prompt to get (defaults to latest).
+        :returns: A Prompt resource.
+        """
+        ...
+
+    @webmethod(route="/prompts", method="POST", level=LLAMA_STACK_API_V1)
+    async def create_prompt(
+        self,
+        prompt: str,
+        variables: list[str] | None = None,
+    ) -> Prompt:
+        """Create prompt.
+
+        Create a new prompt.
+
+        :param prompt: The prompt text content with variable placeholders.
+        :param variables: List of variable names that can be used in the prompt template.
+        :returns: The created Prompt resource.
+        """
+        ...
+
+    @webmethod(route="/prompts/{prompt_id}", method="PUT", level=LLAMA_STACK_API_V1)
+    async def update_prompt(
+        self,
+        prompt_id: str,
+        prompt: str,
+        version: int,
+        variables: list[str] | None = None,
+        set_as_default: bool = True,
+    ) -> Prompt:
+        """Update prompt.
+
+        Update an existing prompt (increments version).
+
+        :param prompt_id: The identifier of the prompt to update.
+        :param prompt: The updated prompt text content.
+        :param version: The current version of the prompt being updated.
+        :param variables: Updated list of variable names that can be used in the prompt template.
+        :param set_as_default: Set the new version as the default (default=True).
+        :returns: The updated Prompt resource with incremented version.
+        """
+        ...
+
+    @webmethod(route="/prompts/{prompt_id}", method="DELETE", level=LLAMA_STACK_API_V1)
+    async def delete_prompt(
+        self,
+        prompt_id: str,
+    ) -> None:
+        """Delete prompt.
+
+        Delete a prompt.
+
+        :param prompt_id: The identifier of the prompt to delete.
+        """
+        ...
+
+    @webmethod(route="/prompts/{prompt_id}/set-default-version", method="PUT", level=LLAMA_STACK_API_V1)
+    async def set_default_version(
+        self,
+        prompt_id: str,
+        version: int,
+    ) -> Prompt:
+        """Set prompt version.
+
+        Set which version of a prompt should be the default in get_prompt (latest).
+
+        :param prompt_id: The identifier of the prompt.
+        :param version: The version to set as default.
+        :returns: The prompt with the specified version now set as default.
+        """
+        ...