feat: surface X-Logfire-Warning header

[adriangb]

Gives the Logfire backend an out-of-band channel — independent of response bodies — to deprecate endpoints or signal hard failures to any client running this SDK.

A new logfire/_internal/server_response.py module installs a requests response hook on every Logfire-bound HTTP session (OTLP exporters, token validation, CRUD client, variables provider, CLI). Each Logfire response is checked for the custom headers X-Logfire-Warning: <message> which calls warnings.warn(message, LogfireServerWarning). Python's default filter dedupes identical messages within a process, so a chatty server only warns once.

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[cubic-dev-ai]

No issues found across 7 files

Confidence score: 5/5

• Automated review surfaced no issues in the provided summaries.
• No files require special attention.

[cubic-dev-ai]

1 issue found across 5 files (changes from recent commits).

Prompt for AI agents (unresolved issues)

Check if these issues are valid — if so, understand the root cause of each and fix them. If appropriate, use sub-agents to investigate and fix each issue separately.


<file name="logfire/_internal/config.py">

<violation number="1" location="logfire/_internal/config.py:1333">
P2: `_lazy_init_variable_provider` (line 1462) creates a `LogfireRemoteVariableProvider` without passing `transport_response_hook`, so lazily-initialized providers won't surface server warning/error headers. Add `transport_response_hook=self.advanced.transport_response_hook` there as well.</violation>
</file>

_{Reply with feedback, questions, or to request a fix. Tag @cubic-dev-ai to re-run a review.}

[cubic-dev-ai]

2 issues found across 6 files (changes from recent commits).

Prompt for AI agents (unresolved issues)

Check if these issues are valid — if so, understand the root cause of each and fix them. If appropriate, use sub-agents to investigate and fix each issue separately.


<file name="logfire/_internal/config.py">

<violation number="1" location="logfire/_internal/config.py:222">
P3: The new callback example uses an undefined variable (`response`) instead of the `helper` parameter.</violation>
</file>

<file name="logfire/_internal/server_response.py">

<violation number="1" location="logfire/_internal/server_response.py:42">
P2: Use an explicit `None` check for `hook`; truthiness can skip valid custom callbacks and unexpectedly run the default hook.</violation>
</file>

_{Tip: Review your code locally with the cubic CLI to iterate faster.}

[cubic-dev-ai]

1 issue found across 5 files (changes from recent commits).

Prompt for AI agents (unresolved issues)

Check if these issues are valid — if so, understand the root cause of each and fix them. If appropriate, use sub-agents to investigate and fix each issue separately.


<file name="logfire/types.py">

<violation number="1" location="logfire/types.py:291">
P1: `default_hook()` no longer processes `X-Logfire-Error`, so server-signaled hard failures are ignored.</violation>
</file>

_{Tip: Review your code locally with the cubic CLI to iterate faster.}