Statement-level edits for raw Workshop: insert, replace, delete with canonical emission #532

Part of wrightkit/wright#838. Implements the workshop-rs side of wrightkit/wright ADR-0029 decisions 2, 3 and 5 (write direction). Required by wrightkit/wright#834.

Desired behavior

For a parsed raw Workshop program, the owner produces the checked SourceEdit that inserts statements before, replaces, or deletes the statement at a statement address (rule, list = conditions or actions, index), including each emitted statement's canonical text in the session's resolved Workshop locale, its indentation relative to the surrounding source, statement comments, and creation of a missing section.

Scope

• A public statement-edit call built on Program::edit_source; bytes outside an edit are unchanged and failures are fail-closed.
• insert takes a non-empty statement list placed before index (index equal to the list length appends); replace takes one statement; delete takes none.
• replace keeps the replaced statement's leading comment; delete removes the statement with its comment; insert writes none.
• Inserting into a rule with no conditions section creates the section. After deleting the last statement the rule reparses with an empty list; whether the empty section stays in the text is decided here.
• A rule whose other content the export cannot express still accepts an insert or an edit to a different statement.

Non-goals

Rule-level edits, variable and subroutine declarations, settings, creating or editing comments, OverPy and OSTW authoring.

Constraints

• Depends on Convert a rule-content-v1 statement into the public model #531 (content-to-model conversion, the input to this call).
• Wright ADR-0029 decision 5: an edited statement is emitted canonically, so its spelling may differ from the replaced one; nothing outside it changes.
• The exact Rust API, error ids and indentation rules belong to this repository.

Acceptance criteria

• Round trip: for every statement the corpora parse and the export can express, content(parse(emit(statement_from_content(c)))) == c, in every supported Workshop locale.
• Insert, replace, and delete at the start, middle, and end of a list each leave all bytes outside the edit unchanged and reparse to the expected content.
• A replaced or deleted statement's comment is kept or removed as specified; an inserted statement has none.
• Insert into an absent conditions section creates it; delete of the last statement reparses with an empty list.
• Statements are emitted in the locale passed in, with en-US and zh-CN coverage, including a rule whose neighbours use that locale.
• A stale or out-of-range address is refused without producing an edit.

Related

wrightkit/wright#834, wrightkit/wright ADR-0029.