#2599 gatorwalk-factory: graph validation and exhaustive check (GW-9)

Part of the gatorwalk-factory rebuild of @swamp/software-factory. Depends only on GW-2 (shipped in #2576), so it can run in parallel with GW-5.

GW-2's schema checks each lifecycle's shape and references when it is saved. GW-9 adds the analysis of the lifecycle as a graph, so an author finds a design problem before a work item hits it:

• stages unreachable from the initial stage;
• stages from which no terminal stage can be reached (dead ends);
• ambiguous exits: two transitions from a stage that can be satisfied together with no human choice between them (the propulsion rule would have to guess);
• loops with no way out except abandon, and loops whose only bound is the default cycle limit;
• transitions whose gates can never pass (e.g. evidence-recorded on evidence the stage does not record, since that gate only accepts evidence from the current stage and cycle);
• wiring for stage plugins: every contract exit goes somewhere, and a plugin's inputs are produced on every path that reaches it.

The exhaustive check explores the lifecycle's reachable states with gate outcomes abstracted, and reports the paths behind each problem. Output is structured (errors and warnings with paths) for the local design page (GW-10) and the authoring skill. The shipped build-swamp-extension lifecycle and the testdata fixtures must pass, or each finding must be explained.

Out of scope: the HTML page (GW-10), plugin composition (GW-12). Nothing is published.