document-for-agents: the doc-cache lifecycle

Documentation is a cache of the codebase: it stores what re-deriving from code would cost. Caches have a coherence problem: entries go stale, and a stale entry misleads with confidence where an empty cache would force a read of the source. The lifecycle has two equal outputs: cache accuracy, keeping the tree true to the code, and attention control, resolving only the relevant sources an agent needs through a runtime orientation resolver (ADR-0024, ADR-0032). This skill runs both, and it keeps the cache's tier matched to the project as the project grows (ADR-0028).

A seam is a module with one distinct responsibility that an agent edits as a unit: its own directory, entry files, tests, and, once the tree is established, its own leaf doc.

Principles: every branch obeys these