test(core-components): cover use_double_brackets toggle in prompt template

[Victor-w-Madeira]

Summary

• Adds prompt-template-double-brackets-regression with 5 @stable tests exercising the use_double_brackets toggle and the mustache code path on the Prompt Template component.
• Cross-links the new spec from the existing prompt-template-component-regression.md doc and extends the §3.2 entries in QA-CHECKLIST.md.
• All 5 tests pass locally against nightly (23s end-to-end); typecheck + ESLint pass with 0 errors and no new warnings.

Scope of coverage

#	Test	Validates
1	Toggle is exposed in the InspectionPanel with its upstream display name	toggle_bool_use_double_brackets is visible after add; "Use Double Brackets" display name renders
2	Default toggle state is OFF; f-string mode extracts {var} and treats {{var}} as literal	Saving Hello {single} and {{double}}! yields exactly one handle (single)
3	Enabling toggle switches parser to mustache mode; {{var}} creates handle and {var} is ignored	Toggle ON → save same template → only double handle
4	Disabling toggle reverts to f-string mode and variables are re-extracted under the new parser	Toggle ON → save {{name}} → toggle OFF → re-save → name handle drops → save {var} → var handle appears
5	use_double_brackets value persists in the autosaved flow	GET /api/v1/flows/{id} returns template.use_double_brackets.value === true after toggle

Notes on scope adjustments from issue #213

Two of the issue's original framings were revised during implementation to match how the UI actually behaves:

• The info text and the "gated behind advanced options" framing for test 1 do not hold in practice — advanced=True only filters the field from the on-canvas node body via isCanvasVisible(); the InspectionPanel renders the bool toggle directly. The test instead asserts the display name (BoolInput(display_name=...)) is visible. The info string collapses into a hover-tooltip icon when the panel is narrow and is not asserted.
• Test 4 was reframed: empirically the rendered handle set is not reconciled by the toggle alone — update_build_config runs, but the dynamic handles linger until the next save. The test verifies the contract end-to-end (toggle + save) rather than asserting toggle-alone re-extraction.

Both adjustments are documented in docs/core-components/prompt-template-double-brackets-regression.md under Notes.

Test plan

• npm run typecheck — 0 errors
• npm run lint — 0 errors, no new warnings from the new spec
• npx playwright test tests/tests-automations/regression/core-components/prompt-template-double-brackets-regression.spec.ts — 5/5 pass against langflowai/langflow-nightly:latest
• Forced-failure smoke check on test 1 confirms the assertion catches regressions (not always-pass)

Closes #213

[Copilot]

Pull request overview

This PR adds end-to-end Playwright coverage for the Prompt Template component’s use_double_brackets toggle, ensuring both the default f-string parsing path and the mustache parsing path are exercised and documented within the langflow-e2e regression suite.

Changes:

• Adds a new @stable regression spec covering toggle visibility, parser switching behavior, handle extraction semantics, and persisted use_double_brackets state via GET /api/v1/flows/{id}.
• Updates QA documentation to cross-link the new coverage and marks the new scenarios as validated in the checklist.
• Adds a dedicated regression doc describing the new spec’s intent, steps, and upstream dependencies.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
tests/tests-automations/regression/core-components/prompt-template-double-brackets-regression.spec.ts	Adds 5 serial @stable Playwright tests covering use_double_brackets behavior end-to-end, including backend persistence polling.
QA-CHECKLIST.md	Adds five new §3.2 checklist entries pointing to the new spec.
docs/core-components/prompt-template-double-brackets-regression.md	New documentation describing the new regression spec’s scenarios, steps, and dependencies.
docs/core-components/prompt-template-component-regression.md	Cross-links the new spec from the existing Prompt Template regression doc.

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[Victor-w-Madeira]

Addressed in commit 9a2e05f. The bare .first() was indeed not a real scope — the comment claimed scoping while the implementation didn't deliver it. The fix anchors the assertion on the toggle via an XPath ancestor walk:

const labelOwner = page
  .getByTestId("toggle_bool_use_double_brackets")
  .locator("xpath=ancestor::*[contains(., 'Use Double Brackets')][1]");
await expect(labelOwner).toBeVisible();

If the label is renamed and no ancestor of the toggle has the text in its subtree, the locator resolves to zero elements and toBeVisible() fails — which is the regression we want to catch. Force-fail confirmed (substituted a placeholder string and the assertion failed cleanly with element(s) not found).