Fix submit button not restored after example click

[hysts]

Description

Closes: #12974

Fix submit/stop button display not being restored after clicking an example in ChatInterface with run_examples_on_click=False.
The reported issue was with run_examples_on_click=False, but the root cause is a race condition in the event handler structure that is independent of that setting. The fix addresses the underlying race for all cases.

Root cause

_setup_stop_events() registered a separate handler on chatbot.example_select that set submit_btn=False on the textbox. The frontend dispatch loop processes multiple handlers for the same event sequentially, so:

1. Handler 1 (main example chain) runs to completion, then dispatches the restore .then() as an async fire-and-forget call
2. Handler 2 (submit_btn=False from _setup_stop_events) starts immediately after in the next loop iteration
3. The restore and Handler 2 both make concurrent HTTP requests → race condition

With run_examples_on_click=False, the race consistently resulted in submit_btn=False winning (the textbox should never enter processing state at all in this case). With run_examples_on_click=True, the race was less likely to manifest in practice because the longer-running submit_fn shifted timing, but the same structural issue existed.

Changes

1. Removed self.chatbot.example_select from event_triggers — eliminates the separate handler, eliminating the race
2. Added submit_btn=False as a .then() step in the chain (only when run_examples_on_click=True and cache_examples=False) — placed after example_clicked and before submit_fn, keeping it in a single sequential chain so the restore always fires strictly after it
3. Skip events_to_cancel for populate-only examples (run_examples_on_click=False) — no inference runs, so no stop/cancel behavior is needed

AI Disclosure

We encourage the use of AI tooling in creating PRs, but the any non-trivial use of AI needs be disclosed. E.g. if you used Claude to write a first draft, you should mention that. Trivial tab-completion doesn't need to be disclosed. You should self-review all PRs, especially if they were generated with AI.

• I used AI (Claude Code) to identify the root cause through codebase analysis (tracing the frontend dispatch loop and backend event chain) and to generate the fix
• I did not use AI

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Install Gradio from this PR

pip install https://gradio-pypi-previews.s3.amazonaws.com/79a84efc85967adda7e6e4f7cba46bfa36d8250e/gradio-6.8.0-py3-none-any.whl

Install Gradio Python Client from this PR

pip install "gradio-client @ git+https://github.com/gradio-app/gradio@79a84efc85967adda7e6e4f7cba46bfa36d8250e#subdirectory=client/python"

Install Gradio JS Client from this PR

npm install https://gradio-npm-previews.s3.amazonaws.com/79a84efc85967adda7e6e4f7cba46bfa36d8250e/gradio-client-2.1.0.tgz

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🦄 change detected

This Pull Request includes changes to the following packages.

Package	Version
gradio	patch

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• Fix submit button not restored after example click

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✅ Changeset approved by @freddyaboulton

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[freddyaboulton]

Clean fix @hysts ! tysm