Write Python and YAML code for this change. Return exactly three fenced code blocks.

CONTEXT
- enum EnumRequestedResponseShape(StrEnum): UNCONSTRAINED="unconstrained", SINGLE_WORD="single_word", EXACT_LITERAL="exact_literal". Each member line is followed by a one-line docstring string literal.
- Module requested_response_shape.py imports EnumRequestedResponseShape and declares:
  _SHAPE_PRECEDENCE: tuple[EnumRequestedResponseShape, ...] = (
      EnumRequestedResponseShape.EXACT_LITERAL,
      EnumRequestedResponseShape.SINGLE_WORD,
  )
  The resolver takes prompt[:400], tries each shape in that order, and for each pattern calls re.compile(pattern, re.IGNORECASE).search(window); first hit wins, else UNCONSTRAINED.
- Existing YAML directive style (Python re, double-quoted):
  single_word:
    - "in (?:exactly )?one word"
    - "(?:answer|reply|respond) with (?:only )?(?:the |a |one )?single word"

TASK
Add shape LENGTH_CONSTRAINED = "length_constrained", resolved last (after SINGLE_WORD).
Its patterns must MATCH each of:
  "Summarize in one sentence what a Bifrost lane overlay does."
  "Explain in a sentence or two how the ledger lock works."
  "Briefly, describe the runtime train."
  "Describe the deploy agent in 30 words or fewer."
and must NOT match any of:
  "Analyse why the style guide requires one sentence per line in docs."
  "Discuss whether a brief outage justifies a rollback, citing sources."
  "Compare the 30 words or fewer limit in tweets to headline limits."
  "Discuss why one word is rarely enough in technical documentation."
  "Summarise the routing architecture and cite your sources."
Hint: anchor on the instruction phrasing ("in one sentence", "in a sentence or two", "in N words or fewer", a leading "Briefly"), not on bare nouns.

OUTPUT
Block 1 (python): the member line and its docstring line.
Block 2 (python): the complete new _SHAPE_PRECEDENCE assignment, members fully qualified.
Block 3 (yaml): two top-level keys, response_shape_directives with ONLY a length_constrained list, and default_shape_overrides with ONLY length_constrained: {heuristic: [no_refusal, short_form_adequacy]}.
