feat(autofix): aider harness behind AUTOFIX_HARNESS flag (Phase 2a)

Lightweight.Dockerfile

@@ -38,6 +38,20 @@ ENV UV_HTTP_TIMEOUT=300
 RUN uv pip install --system torch==2.2.0 --index-url https://download.pytorch.org/whl/cpu
 RUN uv pip install --system -r requirements.txt
 
+# Aider has a sprawling dep graph (litellm, prompt-toolkit, gitpython, …)
+# that pins different versions of packages we already use. Install it in
+# a dedicated venv so its deps don't fight ours, then symlink the binary
+# onto PATH so `subprocess.run(["aider", ...])` in src/seer/automation/harness/
+# Just Works. Only loaded when AUTOFIX_HARNESS=aider; the default
+# AUTOFIX_HARNESS=builtin path never touches this venv.
+RUN python -m venv /opt/aider-venv \
+ && /opt/aider-venv/bin/pip install --no-cache-dir \
+      aider-chat==0.65.0 \
+      "google-auth>=2.29" \
+      "google-cloud-aiplatform>=1.60" \
+ && ln -s /opt/aider-venv/bin/aider /usr/local/bin/aider \
+ && aider --version
+
 # Copy model files (assuming they are in the 'models' directory)
 COPY models/ models/
 # Copy scripts

src/seer/automation/autofix/components/coding/component.py

@@ -7,14 +7,15 @@
 from seer.automation.agent.agent import AgentConfig, RunConfig
 from seer.automation.agent.client import GeminiProvider, LlmClient
 from seer.automation.agent.models import Message, ToolCall
-from seer.automation.autofix.autofix_agent import AutofixAgent
+from seer.automation.autofix.autofix_agent import AutofixAgent  # noqa: F401
 from seer.automation.autofix.autofix_context import AutofixContext
 from seer.automation.autofix.components.coding.models import CodingOutput, CodingRequest
 from seer.automation.autofix.components.coding.prompts import CodingPrompts
 from seer.automation.autofix.components.root_cause.models import RootCauseAnalysisItem
 from seer.automation.autofix.prompts import format_repo_prompt
 from seer.automation.autofix.tools.tools import BaseTools
 from seer.automation.component import BaseComponent
+from seer.automation.harness import select_orchestrator
 from seer.configuration import AppConfig
 from seer.dependency_injection import inject, injected
 
@@ -141,7 +142,13 @@ def invoke(self, request: CodingRequest) -> None:
             if not memory:
                 memory = self._prefill_initial_memory(request=request)
 
-            agent = AutofixAgent(
+            # AUTOFIX_HARNESS=builtin (default) keeps AutofixAgent; "aider"
+            # delegates to the external coding harness. See harness/aider.py.
+            app_config = self._get_app_config()
+            agent_cls = select_orchestrator(
+                app_config.AUTOFIX_HARNESS, strict=app_config.AUTOFIX_HARNESS_STRICT
+            )
+            agent = agent_cls(
                 tools=tools.get_tools(include_claude_tools=True),
                 config=AgentConfig(interactive=True),
                 memory=memory,

src/seer/automation/autofix/components/root_cause/component.py

@@ -5,7 +5,7 @@
 
 from seer.automation.agent.agent import AgentConfig, RunConfig
 from seer.automation.agent.client import GeminiProvider, LlmClient
-from seer.automation.autofix.autofix_agent import AutofixAgent
+from seer.automation.autofix.autofix_agent import AutofixAgent  # noqa: F401
 from seer.automation.autofix.autofix_context import AutofixContext
 from seer.automation.autofix.components.root_cause.models import (
     MultipleRootCauseAnalysisOutputPrompt,
@@ -16,6 +16,7 @@
 from seer.automation.autofix.prompts import format_repo_prompt
 from seer.automation.autofix.tools.tools import BaseTools
 from seer.automation.component import BaseComponent
+from seer.automation.harness import select_orchestrator
 from seer.configuration import AppConfig
 from seer.dependency_injection import inject, injected
 
@@ -42,7 +43,13 @@ def invoke(
 
             sentry_sdk.set_tag("is_rethinking", len(request.initial_memory) > 0)
 
-            agent = AutofixAgent(
+            # AUTOFIX_HARNESS=builtin (default) keeps AutofixAgent; "aider"
+            # delegates to the external coding harness — see harness/aider.py
+            # and docs/coding-harnesses.md.
+            agent_cls = select_orchestrator(
+                config.AUTOFIX_HARNESS, strict=config.AUTOFIX_HARNESS_STRICT
+            )
+            agent = agent_cls(
                 tools=(tools.get_tools(can_access_repos=bool(readable_repos))),
                 config=AgentConfig(
                     interactive=True,

src/seer/automation/autofix/components/solution/component.py

@@ -7,14 +7,15 @@
 from seer.automation.agent.agent import AgentConfig, RunConfig
 from seer.automation.agent.client import GeminiProvider, LlmClient
 from seer.automation.agent.models import Message, ToolCall
-from seer.automation.autofix.autofix_agent import AutofixAgent
+from seer.automation.autofix.autofix_agent import AutofixAgent  # noqa: F401
 from seer.automation.autofix.autofix_context import AutofixContext
 from seer.automation.autofix.components.root_cause.models import RootCauseAnalysisItem
 from seer.automation.autofix.components.solution.models import SolutionOutput, SolutionRequest
 from seer.automation.autofix.components.solution.prompts import SolutionPrompts
 from seer.automation.autofix.prompts import format_repo_prompt
 from seer.automation.autofix.tools.tools import BaseTools
 from seer.automation.component import BaseComponent
+from seer.automation.harness import select_orchestrator
 from seer.configuration import AppConfig
 from seer.dependency_injection import inject, injected
 
@@ -123,7 +124,12 @@ def invoke(
             has_tools = bool(readable_repos)
             repos_str = format_repo_prompt(readable_repos, unreadable_repos)
 
-            agent = AutofixAgent(
+            # AUTOFIX_HARNESS=builtin (default) keeps AutofixAgent; "aider"
+            # delegates to the external coding harness. See harness/aider.py.
+            agent_cls = select_orchestrator(
+                config.AUTOFIX_HARNESS, strict=config.AUTOFIX_HARNESS_STRICT
+            )
+            agent = agent_cls(
                 tools=tools.get_tools() if has_tools else None,
                 config=AgentConfig(interactive=True),
                 memory=memory,

src/seer/automation/harness/__init__.py

@@ -0,0 +1,94 @@
+"""Pluggable autofix orchestrators.
+
+The default orchestrator is the in-process ``AutofixAgent`` (a ReAct loop
+calling Gemini via the existing ``LlmClient``). Alternate orchestrators
+("harnesses") wrap external coding agents like ``aider`` as a subprocess
+and let them propose a patch given the same prompt + repo context.
+
+Selection happens at autofix-component construction time via
+``select_orchestrator(name, strict=...)``. Harness modules register
+themselves at import time with ``register_harness("name", Cls)``.
+
+See ``docs/coding-harnesses.md`` for the rollout plan.
+"""
+
+import logging
+from typing import Protocol, Type, runtime_checkable
+
+from seer.automation.agent.agent import RunConfig
+from seer.automation.autofix.autofix_agent import AutofixAgent
+
+logger = logging.getLogger(__name__)
+
+
+@runtime_checkable
+class AutofixOrchestrator(Protocol):
+    """Anything a component can invoke to drive an autofix step.
+
+    Must support ``.run(run_config=RunConfig(...))`` and return whatever
+    ``AutofixAgent.run`` returns today (a response object with ``.message``,
+    ``.usage``, ``.metadata`` — see ``automation.agent.models``).
+    """
+
+    def run(self, run_config: RunConfig): ...
+
+
+class HarnessNotAvailableError(RuntimeError):
+    """Raised when ``AUTOFIX_HARNESS_STRICT=True`` and the requested
+    harness is unknown or unimportable. Operators using strict mode want
+    a hard failure rather than a silent fallback.
+    """
+
+
+_REGISTRY: dict[str, Type[AutofixOrchestrator]] = {
+    "builtin": AutofixAgent,
+}
+
+
+def register_harness(name: str, cls: Type[AutofixOrchestrator]) -> None:
+    """Used by harness modules at import time to register themselves.
+
+    Re-registering the same ``cls`` under the same ``name`` is a no-op
+    (pytest / module reloads commonly re-import). Registering a *different*
+    class under an existing name raises ``ValueError`` so two modules
+    can't silently clobber each other.
+    """
+    existing = _REGISTRY.get(name)
+    if existing is cls:
+        return
+    if existing is not None:
+        raise ValueError(
+            f"Harness '{name}' is already registered as "
+            f"{existing.__name__}; remove the duplicate registration."
+        )
+    _REGISTRY[name] = cls
+
+
+def select_orchestrator(harness_name: str, strict: bool = False) -> Type[AutofixOrchestrator]:
+    """Resolve ``AppConfig.AUTOFIX_HARNESS`` to an orchestrator class.
+
+    When the requested harness isn't registered:
+      * ``strict=False`` (default): log a warning and return the builtin.
+      * ``strict=True``: raise ``HarnessNotAvailableError``.
+
+    The fallback prevents a typo or a missing optional dep from disabling
+    autofix outright.
+    """
+    if harness_name in _REGISTRY:
+        return _REGISTRY[harness_name]
+    msg = f"Unknown AUTOFIX_HARNESS={harness_name!r}; " f"known: {sorted(_REGISTRY)}"
+    if strict:
+        raise HarnessNotAvailableError(msg)
+    logger.warning("%s — falling back to 'builtin'.", msg)
+    return _REGISTRY["builtin"]
+
+
+# Eagerly import optional harness modules so their import-time
+# register_harness() side-effects run. Wrapped in a try/except so a
+# missing optional dep (e.g. aider-chat not pip-installed) doesn't
+# break `from seer.automation.harness import select_orchestrator`
+# for the builtin path.
+try:
+    from . import aider as _aider  # noqa: F401, E402
+except ImportError as exc:  # pragma: no cover
+    logger.debug("Optional aider harness not importable: %s", exc)