Fold the August fleet findings into the policies, or drop them (closes #62)

Of the cross-repository findings recorded on 2026-08-09, two were rules a repository must follow that `prompts/REPO_POLICIES.md` did not yet state, and each now sits in the paragraph a reader would be in. A new or changed check is proven by planting a defect it must catch and watching the run fail, since a green run alone does not show the check ran. A separate workflow limited to `main` by a `branches` list is first run from the feature branch by adding that branch to the list and removing it before merging, with any publishing job kept behind `if: github.ref_name == 'main'`.

The other findings are dropped, each with its reason on the issue; the `config verify` warning goes by sneak's ruling on #40 that there is no config check step.

Model: opus-5-5

TODO.md

@@ -21,6 +21,17 @@ fmt-check, and commit.
 
 # Completed Steps
 
+- 2026-10-04: Went through the fleet findings recorded on 2026-08-09 (issue 62)
+  and added the two rules `REPO_POLICIES.md` did not yet state: a new or changed
+  check is proven by planting a defect it must catch; and a change to a separate
+  workflow limited to `main` is first run from the feature branch, added to that
+  workflow's `branches` list and removed again before merging. The other
+  findings were already stated, replaced by `--no-cache`, about git worktrees,
+  or about how agents work together. The warning against
+  `golangci-lint config verify` is dropped because sneak ruled on
+  https://git.eeqj.de/sneak/prompts/issues/40 (2026-08-10) that there is no
+  config check step and the config is assumed valid; a vendored `.golangci.yml`
+  stays byte-identical to the canonical copy. The issue gives each reason.
 - 2026-10-04: `REPO_POLICIES.md` now says which `Dockerfile` stages run
   `script/bootstrap` (issue 90). The gate phases and the build stage start from
   their pinned base images and install what those images lack either inline, as

prompts/REPO_POLICIES.md

@@ -160,6 +160,9 @@ style conventions are in separate documents:
   not evidence that anything ran: a sub-second build reporting success is a
   cache hit, not a result. Never invalidate by pruning — `docker builder prune`
   and friends destroy a build cache shared with every other build on the host.
+  When a check is added or changed, prove it works by planting a defect it must
+  catch and watching the run fail on it, then revert the defect. A green run
+  alone shows neither that the check ran nor that it covers what it should.
 
 - **The gate phases are separate stages, and the build stage depends on both.**
   The lint phase is based on the `golangci/golangci-lint` image (pinned by
@@ -283,7 +286,12 @@ style conventions are in separate documents:
   carry the same guarantee, because its gate phases may come from the cache. The
   image build is uncached and so runs the gate phases a second time. That is the
   price of the rule above, and it is worth paying: the image that ships is built
-  from a run of its own gates rather than from a cache entry.
+  from a run of its own gates rather than from a cache entry. A separate
+  workflow limited to `main` by a `branches` list under `on: push` cannot be
+  checked by review: to try a change to it, add the feature branch to that list
+  and push, then remove the branch from the list again before merging. Keep any
+  job in it that publishes behind `if: github.ref_name == 'main'`, so the run
+  from the feature branch publishes nothing.
 
 - Use platform-standard formatters: `black` for Python, `prettier` for
   JS/CSS/Markdown/HTML, `go fmt` for Go. Always use default configuration with