feat(intent): a child collection can outlive its master's lock

[delchev]

Problem

An issued invoice cannot be settled by hand.

immutableWhen on the master puts the document page into read-only mode, and the generated UI extends that lock over every child panel — so the Add button and the row actions on Sales Invoice Customer Payments exist only while the invoice is DRAFT. Manual allocation is unavailable in exactly the state where allocations mean something, and a payment record has no allocation screen of its own, so there is no other route.

The UI was enforcing a rule the model never declared

Verified against a live instance, with the invoice ISSUED:

check	result
GET /{id}/mutable on the master	{"mutable": false}
PUT the master header	409
POST an allocation to the child controller	200
invoice after it	Paid 0 → 20, Balance 80, status → PARTIAL

The child is a different entity, with its own controller and no immutability of its own. The server always permitted these writes — only the affordance was missing.

Change

locksWithMaster: false on a composition child states it in the model:

- name: SalesInvoiceCustomerPayment
  locksWithMaster: false      # settlement is not part of the frozen document

Settlement is a different lifecycle from content: an issued invoice's lines are frozen, money keeps arriving against it for months.

The parser validates both halves rather than ignoring a misplaced flag — it must be a composition child, and its master must actually lock. An inert declaration reads exactly like a working one, and the author would otherwise only discover it when the affordance was still missing in production.

Emitted (and consumed) only when false, so every existing model regenerates byte-identically. Relaxes the three gates on the document view and the same three on the manage form view. A document's own line items are unaffected — they render in the items pane, not a child panel, and stay locked.

Tests

• EdmIntentGeneratorTest — the marker lands on the child, and on neither the master nor the line items.
• IntentParserTest — both rejections (not a composition child; master never locks) and the valid shape.
• Full engine-intent suite: 148 green.
• The registry emission rendered through a real Velocity engine both ways: absent → nothing, false → locksWithMaster: false.

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