[Feature request] New Agent (beta): composer UI to declare app variables so webapp URL pre-fill works like Chatflow's Hidden & Pre-Filled fields

[xiongyidxx]

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1. Is this request related to a challenge you're experiencing? Tell me about your story.

We publish an internal assistant as a standalone new Agent app (mode agent, beta) on self-hosted 1.17.0, and external systems (intranet portals) need to hand off context (e.g. expense report id, user identity) into the published webapp URL.

On Chatflow apps this is a first-class flow: mark User Input fields as Hidden & Pre-Filled, then share {WEBAPP_URL}?{VAR}={VALUE} — the official docs even describe generating such links in bulk from a third-party system.

On a standalone Agent app I could not find any way to declare input variables. I was trying to pre-fill variables via /agent/<token>?var=value, and nothing happened: GET /parameters returns an empty user_input_form, the opening form never renders, and the URL params are silently dropped by the backend whitelist filter (api/core/app/apps/base_app_generator.py:124-137). It's frustrating because everything downstream of the config already works — only the declaration UI is missing.

2. Additional context or comments

Source findings on 1.17.0 (the plumbing is already in place):

• Contract exists: AppVariableConfig { name, type, required, default } — packages/contracts/generated/api/console/agent/types.gen.ts:1016-1021, referenced as app_variables on the Agent Soul config (:584).
• Runtime projection exists: Agent Soul app_variables → user_input_form — api/core/app/apps/agent_app/app_config_manager.py:113 (served by GET /parameters).
• Webapp rendering exists, with no agent-specific gating: plain-text URL query params are consumed at web/app/components/base/chat/chat-with-history/hooks.tsx:331-339 (getRawInputsFromUrlParams); the opening form renders whenever user_input_form is non-empty (chat-wrapper.tsx:349-358); values are submitted as inputs with POST /chat-messages.
• The console preview adapter already maps app_variables to input-form types — web/features/agent-v2/agent-detail/configure/components/preview/chat-config.ts:100-107,123-124,206-215.
• The missing piece: web/features/agent-v2/agent-composer/store-modules/ has no app-variables module (only app-features/env/files/knowledge/model/prompt/skills/tools), so app_variables can currently only be set via DSL import / console API.

Suggested solution: add an "App variables" section to the Agent composer — types text-input / paragraph / select / number / json (same mapping the preview adapter already uses), plus a per-field "hidden & pre-filled" toggle — persisted to Agent Soul app_variables. That alone unlocks URL query pre-fill on /agent/[token] webapps with no further changes.

Related: #41779 (binding declared variables to tool parameters).

3. Can you help us with this feature?

• I am interested in contributing to this feature.