fix(api): accumulate truncated flag in _truncate_array

[agarwalpranav0711]

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Summary

Fixes #39773

_truncate_array in api/services/variable_truncator.py uses a direct assignment (truncated = part_result.truncated) at line 304, which overwrites the truncation flag on every loop iteration. If an early array element is truncated but a later one fits within budget, the method incorrectly returns truncated = False.

The other two methods in the same file accumulate the flag correctly:

• truncate_variable_mapping (line 136): is_truncated = is_truncated or part_result.truncated
• _truncate_object (lines 383-384): if value_result.truncated: truncated = True

This PR applies the same accumulating pattern to _truncate_array and adds a targeted unit test.

Changes

• api/services/variable_truncator.py: Changed truncated = part_result.truncated → truncated = truncated or part_result.truncated
• api/tests/unit_tests/services/test_variable_truncator.py: Added test_array_truncation_flag_accumulation to verify the flag stays True when an early element is truncated but a later one is not

Screenshots

N/A — backend-only logic fix, no UI changes.

Checklist

• This change requires a documentation update, included: Dify Document
• I understand that this PR may be closed in case there was no previous discussion or issues. (This doesn't apply to typos!)
• I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change.
• I've updated the documentation accordingly.
• I ran make lint && make type-check (backend) and cd web && pnpm exec vp staged (frontend) to appease the lint gods

[github-actions]

Pyrefly Diff

base → PR

--- /tmp/pyrefly_base.txt	2026-07-29 17:25:08.033178936 +0000
+++ /tmp/pyrefly_pr.txt	2026-07-29 17:24:58.714097611 +0000
@@ -8397,11 +8397,11 @@
 ERROR Cannot set item in `dict[str, int]` [unsupported-operation]
    --> tests/unit_tests/services/test_variable_truncator.py:142:31
 ERROR Argument `list[File]` is not assignable to parameter `value` with type `list[object]` in function `services.variable_truncator.VariableTruncator._truncate_array` [bad-argument-type]
-   --> tests/unit_tests/services/test_variable_truncator.py:724:44
+   --> tests/unit_tests/services/test_variable_truncator.py:731:44
 ERROR Argument `list[File]` is not assignable to parameter `value` with type `list[object]` in function `services.variable_truncator.VariableTruncator._truncate_array` [bad-argument-type]
-   --> tests/unit_tests/services/test_variable_truncator.py:736:44
+   --> tests/unit_tests/services/test_variable_truncator.py:743:44
 ERROR Argument `list[File]` is not assignable to parameter `value` with type `list[object]` in function `services.variable_truncator.VariableTruncator._truncate_array` [bad-argument-type]
-   --> tests/unit_tests/services/test_variable_truncator.py:751:44
+   --> tests/unit_tests/services/test_variable_truncator.py:758:44
 ERROR Argument `dict[str, dict[Unknown, Unknown]]` is not assignable to parameter `node_config` with type `NodeConfigDict` in function `services.trigger.webhook_service.WebhookService.generate_webhook_response` [bad-argument-type]
    --> tests/unit_tests/services/test_webhook_service.py:250:79
 ERROR Argument `dict[str, dict[str, int | str]]` is not assignable to parameter `node_config` with type `NodeConfigDict` in function `services.trigger.webhook_service.WebhookService.generate_webhook_response` [bad-argument-type]

[github-actions]

Pyrefly Type Coverage

Metric	Base	PR	Delta
Type coverage	56.46%	56.46%	-0.00%
Strict coverage	55.97%	55.97%	-0.00%
Typed symbols	36,871	36,872	+1
Untyped symbols	28,686	28,687	+1
Modules	3091	3091	0