activePullRequest tool doesn't recognize PR from suggested context

[zhichli]

Testing #280380

Steps to Reproduce:

1. Enable suggested context by setting: "chat.implicitContext.suggestedContext": true
2. Open a PR from the Pull Request list panel
3. Observe that the PR appears as suggested context in the chat widget
4. Send a chat request (the PR should appear as an attachment in the chat)

Current Behavior:
The first activePullRequest tool call returns "no active PR" even though the PR info is attached to the user query (visible in chat debug log as an attachment - see screenshot below).

Expected Behavior:
One of the following should occur:

• Option 1: The activePullRequest tool call should recognize and return the PR info when it's attached as suggested context
• Option 2: The PR should only be sent as an attachment when the user explicitly clicks the "+" button beside the context item (not automatically as suggested context)

Additional Context:
The inconsistency between the UI (showing PR as attachment) and the tool behavior (returning "no active PR") creates confusion about what context is actually being used in the conversation.

Screencast.from.12-02-2025.03.04.54.PM.webm