generate the dashboards at build time instead of committing them

The JSON is machine-written and the generator beside it is the only source of
truth, so committing both only created a way for them to drift -- which is what
the dashboards-current check existed to police. modules/dashboards.nix now runs
gen_zfs.py / gen_smart.py in the derivation, so a stale dashboard cannot be
built at all and the check is gone.

Note there is no third option: flakes copy only git-tracked files into the
store, so a gitignored dashboards/*.json cannot be read from disk either. It is
generate, or commit.

Verified equivalent -- both generated dashboards are byte-identical to the JSON
this commit deletes.

Adds a dashboards-nonempty check. Factoring the shared jq invocation out first
introduced a bug it caught: the multi-line string ended in a newline, so the
callers' `< $src > "$out"` landed on a line of its own as a separate command,
truncating every dashboard to zero bytes while the build still succeeded. All
four provisioned dashboards were empty. jqFixup is now a single line, and the
check asserts each dashboard is non-empty and has a title, uid and panels.

Both failure modes are exercised: an empty dashboard and one with no panels each
fail the check. It also asserts it found four files, because the first version
globbed *.json against linkFarm entries named without the suffix and passed
vacuously.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01JKczN1f66kmLxNBLX37voQ

1 files changed, 9 insertions, 8 deletions

diff --git a/README.md b/README.md
index 7bcea7f..9014e1b 100644
--- a/README.md
+++ b/README.md
@@ -17,8 +17,7 @@ What *has* been checked:
 
 - every dashboard query executed against a real Prometheus fed fixture data
 - `promtool` over the recording rules and the generated scrape config
-- `nix flake check`: both modules evaluate, and the committed dashboard JSON matches what
-  the generators produce
+- `nix flake check`: both modules evaluate, and both dashboard generators run
 - the collectors run against mock `smartctl`/`zpool`/`zfs`, and partially against real
   hardware
 
@@ -225,21 +224,23 @@ modules/
   dashboards.nix        builds dashboard JSON into a provisionable form
   packages.nix          the two collectors as ordinary packages
 collectors/*.py         the collectors themselves; runnable by hand
-dashboards/gen_*.py     dashboard generators
-dashboards/*.json       generated, committed, checked
+dashboards/gen_*.py     dashboard generators; the JSON is built, not committed
 rules/smartctl.yml      Prometheus recording rules
 ```
 
 ## Working on it
 
-Dashboard JSON is **generated** — edit `dashboards/gen_*.py`, never the JSON:
+The ZFS Pools and Drive Health dashboards are **generated at build time** from
+`dashboards/gen_*.py`; no JSON is committed, so there is nothing to keep in sync and no
+way to ship a stale dashboard. To see what a generator currently produces:
 
 ```sh
-python3 dashboards/gen_zfs.py   > dashboards/zfs-pools.json
-python3 dashboards/gen_smart.py > dashboards/smart.json
+python3 dashboards/gen_zfs.py   | less
+nix build .#nixosConfigurations.<host>.config.system.build.toplevel   # or just deploy
 ```
 
-`nix flake check` fails if you forget.
+(Flakes copy only git-tracked files into the store, so "gitignore the JSON and read it
+from disk anyway" is not an option — it is generate, or commit.)
 
 The collectors are plain scripts taking `--output PATH`, so you can see exactly what a
 machine reports: