Add PipelineDehydrator(extract_subgraphs=False) seam (v0.1.30)

[Volv-G]

(AI-assisted)

Part 1 of 2 in a stack. Part 2: #76 (YAML→Python decompiler, v0.1.31), based on this branch.

What

A keyword-only PipelineDehydrator(extract_subgraphs: bool = True) option, plus the v0.1.30 version bump.

False keeps every nested-graph boundary inline and dehydrates only the leaf components inside it, in place. It is for callers that represent nested graphs themselves; the decompiler in part 2 turns each one into a Python @pipeline.

Evidence

• The default is True, so ordinary dehydration and pipelines dehydrate are byte-for-byte unchanged. No existing test line is changed or removed.
• One new parametrized test covers DIGEST, FILE and AUTO: the boundary stays inline, the leaf is dehydrated, and no subgraph file is written.

How

The new branch sits in dehydrate() before the existing AUTO/FILE/URL and DIGEST/NAME subgraph-extraction branches, which are otherwise unchanged.

Failure modes

Only callers that pass extract_subgraphs=False are affected, and they get a deliberately not-fully-dehydrated document.

Testing

• 3.10 and 3.12 full non-packaging suites: 2090 passed each.
• Packaging: 10/10. Locally this needed the uv index config bypassed; that is a local issue, not a repo one.
• ruff: clean on the touched files. The repo-wide count is 36, the same as master.
• git diff --check: clean.
• Independent local review found no blocking findings (option-ignored mutant killed).

Review focus

The option's semantics and its placement in dehydrate().