fix(litellm): Guard against module shadowing

[alexander-alderman-webb]

Description

Use explicit imports to prevent AttributeError when litellm is shadowed.

Issues

Follows up on #5140.

Reminders

• Please add tests to validate your changes, and lint your code using tox -e linters.
• Add GH Issue ID & Linear ID (if applicable)
• PR title should use conventional commit style (feat:, fix:, ref:, meta:)
• For external contributors: CONTRIBUTING.md, Sentry SDK development docs, Discord community

[sentry]

Bug: User-configured LiteLLM callbacks are overwritten during Sentry initialization if they are set before sentry_sdk.init() is called, due to using stale, import-time references.
_{Severity: MEDIUM | Confidence: High}

🔍 Detailed Analysis

The change imports input_callback, success_callback, and failure_callback from litellm at the module level, capturing their state at import time. If a user sets their own litellm callbacks after the import but before sentry_sdk.init() is called, the setup_once function will use the stale, import-time values (empty lists) to re-assign the callbacks. This overwrites and silently discards the user's pre-configured callbacks, preventing them from running. This behavior is a regression from the previous implementation which read the current callback values.

💡 Suggested Fix

In setup_once, instead of using the variables imported at the module level, access the callbacks directly from the litellm module to get their current values. For example, use litellm.input_callback = litellm.input_callback or [] to preserve any user-set callbacks.

🤖 Prompt for AI Agent

Review the code at the location below. A potential bug has been identified by an AI
agent.
Verify if this is a real issue. If it is, propose a fix; if not, explain why it's not
valid.

Location: sentry_sdk/integrations/litellm.py#L279-L292

Potential issue: The change imports `input_callback`, `success_callback`, and
`failure_callback` from `litellm` at the module level, capturing their state at import
time. If a user sets their own `litellm` callbacks after the import but before
`sentry_sdk.init()` is called, the `setup_once` function will use the stale, import-time
values (empty lists) to re-assign the callbacks. This overwrites and silently discards
the user's pre-configured callbacks, preventing them from running. This behavior is a
regression from the previous implementation which read the current callback values.

_{Did we get this right? 👍 / 👎 to inform future reviews.
Reference ID: 7692173}

[alexander-alderman-webb]

fair point, but by design sentry_sdk.init() should be initialized first.