docs: add form interaction guidance

SKILL.md

@@ -68,6 +68,7 @@ If you start struggling with a specific mechanic while navigating, look in inter
 - downloads.md
 - drag-and-drop.md
 - dropdowns.md
+- forms.md
 - iframes.md
 - network-requests.md
 - print-as-pdf.md
@@ -112,7 +113,7 @@ If you start struggling with a specific mechanic while navigating, look in inter
 - After every meaningful action, re-screenshot before assuming it worked. Use the image to verify changed state, open menus, navigation, visible errors, and whether the page is in the state you expected.
 - Use screenshots to drive exploration. They are often the fastest way to find the next click target, notice hidden blockers, and decide if a selector is even worth writing.
 - Prefer compositor-level actions over framework hacks. Try screenshots, coordinate clicks, and raw key input before adding DOM-specific workarounds.
-- If you need framework-specific DOM tricks, check interaction-skills/ first. That is where dropdown, dialog, iframe, shadow DOM, and form-specific guidance belongs.
+- If you need framework-specific DOM tricks, check interaction-skills/ first. That is where dropdown, dialog, form/input, iframe, shadow DOM, and other mechanic-specific guidance belongs.
 
 ## Domain skills (opt-in)
 

interaction-skills/forms.md

@@ -0,0 +1,55 @@
+# Forms and framework-managed inputs
+
+Modern frameworks often keep form state outside the DOM. A visible
+`input.value` update can still leave React controlled inputs, Vue `v-model`, or
+Ember/Glimmer tracked state unchanged, so submit buttons stay disabled or click
+handlers no-op.
+
+## Default helper
+
+Use `fill_input(selector, text, clear_first=True, timeout=...)` before falling
+back to lower-level typing:
+
+```python
+fill_input("#email", "agent@example.com", timeout=5)
+click_at_xy(save_x, save_y)
+wait_for_network_idle()
+```
+
+`fill_input()` focuses the element, clears it with the platform select-all
+shortcut, types via CDP key events, and then fires bubbling `input` and `change`
+events. That covers most framework-managed controls better than `type_text()`,
+which uses `Input.insertText` and can bypass framework listeners.
+
+## Modal forms
+
+For modal forms, verify three things after filling:
+
+1. The text is visibly present in a screenshot.
+2. The submit/save button changed state if it was initially disabled.
+3. Clicking submit produces the expected UI change or network activity.
+
+```python
+fill_input("input[name='search']", "cats", timeout=5)
+capture_screenshot("/tmp/form-filled.png")
+click_at_xy(save_x, save_y)
+assert wait_for_network_idle(timeout=10)
+```
+
+## When DOM value and framework state diverge
+
+If `document.querySelector(selector).value` is correct but submit still no-ops:
+
+- Re-click/focus the field visually and retry `fill_input()`; some components
+  ignore events unless focus came from the browser.
+- Prefer real coordinate clicks for the submit action; synthetic DOM clicks may
+  skip framework or component-library handlers.
+- Inspect disabled/error state in the DOM with `js(...)` before inventing a
+  framework-specific hook.
+- Capture the reusable site-specific path in `agent-workspace/domain-skills/`
+  only after it is proven in the browser.
+
+A public no-auth Ember modal/input target for experiments is
+`https://www.ember-bootstrap.com/components/modal/` → **Custom markup** →
+**Open Modal** → **Search** input → **Save** button. It is useful for testing
+modal focus and input mechanics without a LinkedIn account.