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20. Pack: web.fill_form

Status: Accepted Date: 2026-04-07 Domain: api-design

Context​

Form submission against authenticated SaaS apps requires session management, vault credential injection, field detection, value entry, submission, and confirmation — a high-failure-rate workflow for weak models (PRD §6.6).

Decision​

Ship web.fill_form as a built-in pack.

Input: { url: string, credential_id?: string, field_map: object<string, string>, submit_selector?: string, confirm_selector?: string } Output: { success: boolean, final_url: string, confirmation_text?: string } Errors: auth_failed, not_found, schema_mismatch, timeout, network_error

The handler optionally injects credentials, navigates to the form, maps each field_map key to an input via CSS selector / name / id / aria-label, types values, clicks submit, and waits for the confirm selector or URL change. Returns success only if confirmation is observed.

Consequences​

Positive: form submission becomes a single declarative call; credential never exposed. Negative: dynamic forms with conditional fields require per-site overrides.

§6.6 Capability Packs, §14 Credential Vault