The GitHub Actions job "Tests AMD/ARM" on airflow.git/render-template has 
failed.
Run started by GitHub user kaxil (triggered by kaxil).

Head commit for run:
ad77ee62844f40a1dc0e8a2883dac0f7974dbc0a / Kaxil Naik <[email protected]>
Display custom labels for mapped tasks during execution

Currently, custom labels defined via `map_index_template` for mapped tasks
are only rendered and displayed in the UI after task completion. This means
users see only numeric indices (0, 1, 2...) while tasks are running, making
it difficult to identify which specific mapped task instance is executing.

For example, if a mapped task processes different customers, users want to
see "customer_alice" or "customer_bob" in the UI while the task is running,
not just "0" or "1".

The `map_index_template` may reference context
variables set during task execution (e.g., XCom values, return values from
`execute()`, etc.). These variables are only available after the task's
execute method completes, which is why rendering was originally delayed
until task completion.

Example problematic template:
```
"Processing {{ ti.xcom_pull(key='customer_name') }}"
```

or one that access Task Attributes:

```
"Processing {{ task.value }}"
```

This PR implements a two-phase rendering approach:

Phase 1:
- Renders `map_index_template` immediately after template rendering, before
  task execution
- Uses available context variables (task, dag, run_id, logical_date, etc.)
- Sends the rendered label to the API server for immediate UI display
- If rendering fails (e.g., due to missing variables), error is suppressed
  and logged at debug level
- Provides immediate feedback for templates using pre-execution context

Phase 2:
- Re-renders `map_index_template` with full context after task execution
- Includes all execution-time variables (XCom, Task attributes, return values, 
etc.)
- Only sends update if the value changed from Phase 1
- Handles both success and failure cases
- For failures, suppresses rendering errors to avoid masking task errors

For templates with execution-time variables, the label updates after
execution completes with the final rendered value.

Report URL: https://github.com/apache/airflow/actions/runs/18809913121

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