Allow go test on one package while iterating (closes #51)

Follows sneak's ruling at
#51 (comment). An agent
whose work is confined to one package may run `go test` directly on that
package's suite, or on individual tests in it, while iterating. `go build`,
`go vet` and the linter still go through make targets. The full `make check`
is still required before every push. The `Makefile` gains nothing.

The rule on Docker now says the lint and test gates run there, because a run
while iterating is not a gate.

Model: opus-5-5

TODO.md

@@ -21,6 +21,13 @@ fmt-check, and commit.
 
 # Completed Steps
 
+- 2026-11-04: An agent whose work is confined to one package may run `go test`
+  directly on that package's suite, or on individual tests in it, while
+  iterating (https://git.eeqj.de/sneak/prompts/issues/51), on sneak's ruling at
+  https://git.eeqj.de/sneak/prompts/issues/51#issuecomment-167600. The full
+  `make check` is still required before every push, and the `Makefile` gains
+  nothing. The rule on Docker now names the lint and test gates, because a run
+  while iterating is not one.
 - 2026-11-04: node, yarn, npm, python, pip and venv now come from the
   distribution with no version and no hash
   (https://git.eeqj.de/sneak/prompts/issues/146), on sneak's ruling at