Create the pipeline sensitive context when creating a pipeline instance, not on every processing

We used to create the pipeline context during pipeline processing which
means we cannot reuse the same pipeline for output that spans several
data buffers.

Author: jhrozek

src/codegate/pipeline/base.py

@@ -277,6 +277,13 @@ def __init__(
         self.secret_manager = secret_manager
         self.is_fim = is_fim
         self.context = PipelineContext()
+
+        # we create the sesitive context here so that it is not shared between individual requests
+        # TODO: could we get away with just generating the session ID for an instance?
+        self.context.sensitive = PipelineSensitiveData(
+            manager=self.secret_manager,
+            session_id=str(uuid.uuid4()),
+        )
         self.context.metadata["is_fim"] = is_fim
 
     async def process_request(
@@ -290,17 +297,14 @@ async def process_request(
         is_copilot: bool = False,
     ) -> PipelineResult:
         """Process a request through all pipeline steps"""
-        self.context.sensitive = PipelineSensitiveData(
-            manager=self.secret_manager,
-            session_id=str(uuid.uuid4()),
-            api_key=api_key,
-            model=model,
-            provider=provider,
-            api_base=api_base,
-        )
         self.context.metadata["extra_headers"] = extra_headers
         current_request = request
 
+        self.context.sensitive.api_key = api_key
+        self.context.sensitive.model = model
+        self.context.sensitive.provider = provider
+        self.context.sensitive.api_base = api_base
+
         # For Copilot provider=openai. Use a flag to not clash with other places that may use that.
         provider_db = "copilot" if is_copilot else provider