Both halves of `setup` assumed the files they manage are writable. A
declaratively managed target — read-only because a configuration manager
owns it, because a file is flagged immutable, or because the path is
root-owned — made the skill install raise a raw filesystem exception and
the hook install surface the underlying message with no guidance.
Both now fail with `TARGET_NOT_WRITABLE`, naming the file and pointing at
the general remedy: it appears to be managed by another tool, so declare
the skill or hook through that configuration instead. The error names no
particular manager, because read-only is not diagnostic of one.
A target already byte-identical to the bundled copy still succeeds —
nothing needs writing, so its being read-only is beside the point.
Grilling task 0042's mitigation found its framing too narrow. Recording an
absolute entrypoint path is one defect; the deeper one is that `setup` is
write-only, and an operator whose agent configuration is generated
declaratively cannot let it write at all. On such a machine both halves fail —
`setup hooks` against a read-only settings file, and `setup` on an unhandled
filesystem error — and the Agent Skill gets hand-copied into the operator's own
configuration, where it silently drifts from the package that ships it.
Three tasks follow:
- 0043 records the bare binary name, resolved through PATH, so the hook
survives an upgrade on any wrapper-based install. Fixes the marker-substring
coupling with it and drops the derivation's build-tree rename.
- 0044 reports an unwritable target as a structured error naming no cause,
rather than crashing.
- 0045 adds the declarative install path: a stable Skill location, the Skill
and hook specification exposed as Nix-consumable attributes, one committed
hook specification read by both the expression and the test suite, and a
home-manager module wiring them. Blocked by 0043, whose bare name the
specification declares.
CONTEXT.md gains the four terms this settled and amends `setup` and
`SessionStart hook`, which described the imperative path as the only one.
Entries for unbuilt work name the task that lands them, so the glossary does
not assert behaviour the code lacks.
The re-run-after-upgrade help text this branch added stays as it is: accurate
until 0043 removes it, which that task carries as a criterion.
