ci: shorten the PR critical path (desktop lanes, smoke shards, parallel relay artifacts) (#8156)

## Summary

The PR critical path on main push [run
37635224099](https://github.com/block/buzz/actions/runs/37635224099)
(`e097c4299`) was about 42 minutes:

- **Desktop Core** took 41 min. It ran frontend checks, two clippy
graphs, the Tauri suite, the mesh-llm suite and every compiled-flag
state one after another. The compiled-flag step alone took 16m51.
- **Relay artifact producer → Desktop E2E Integration** took about 31
min. The producer built the relay binaries (5m07), the backend
integration archive (4m41) and the PostgreSQL archive (8m18) one after
another.
- **Desktop Smoke E2E** took 19–24 min per shard across 4 shards, with
82 min of tests in total.

This PR attacks all three.

### 1. Run each compiled-flag state once (`Justfile`)

| Previous step | Cost | Why it's redundant |
|---|---|---|
| Clean state: full `buzz_lib` suite (`--lib`) | 3m27 run |
`desktop-tauri-test` runs the same suite in the same compile state one
step earlier. When `BUZZ_TEST_EXPECTED_AGENT_ACCESS_OWNER_ONLY` is
unset, the expected value already defaults to `false` in non-owner-only
builds (`runtime/test_fixtures.rs`, `agents_tests.rs`). |
| Internal state: auto-connect and owner-only built separately | 1m22 +
1m06 + 56s across three recompiles | Internal release packaging always
sets both capabilities together, so building owner-only without
auto-connect tests a configuration that never ships. The extra 56s
happens because a bare `cargo test <filter>` builds every target, not
just the `--lib` harness. |
| Demo state: `cargo test --workspace` | ~30s more than `--lib` |
`buzz-terminal` and the `tests/*.rs` integration tests don't read any
`BUZZ_BUILD_*` variable or `buzz_lib`, so they ran the same binaries a
second time. |

A fourth cost was hidden: every recipe invocation spent ~1m20
recompiling `buzz-desktop` to the *same* unit hash `desktop-tauri-test`
had just built. `_ensure-sidecar-stubs` ran `touch` on every sidecar
stub on each run. `tauri-build` emits `rerun-if-changed` for each
`externalBin`, so the new mtimes reran `build.rs` and recompiled the
crate. Stubs are now created only when they're missing. This also speeds
up any local `desktop-tauri-*` recipe run back-to-back.

After this change:
- **Clean state:** runs only the two compiled-flag assertions
(`compiled_flag_matches_expected`, `compiled_policy_matches_expected`)
with `expected=false`. No recompile.
- **Internal state:** one compile with
`BUZZ_BUILD_AUTO_CONNECT_DEFAULT_RELAY=1` and
`BUZZ_BUILD_AGENT_ACCESS_OWNER_ONLY=1`. It runs both assertions with
`expected=true`, then the full `buzz_lib` suite. The suite now runs with
auto-connect enabled as well, which matches the shipped internal build
more closely than before.
- **Auto-connect-only state (assertions only):** auto-connect `true`,
owner-only `false`. The two capabilities are documented as independent.
Without this state, a `build.rs` block that read the other capability's
variable would pass, because every other state sets both or neither.
- **Demo state:** one compile with only `BUZZ_BUILD_DEMO_SLUG`. It
asserts the slug and asserts both capabilities stay `false`, then runs
the full `buzz_lib` suite.
- The recipe clears the three toggled `BUZZ_BUILD_*` capability
variables and any caller `BUZZ_TEST_EXPECTED_*` values up front. Each
state exports its own values in a subshell. Every invocation uses
`--lib`, so each state compiles one test harness.
- Each ignored-assertion run requires exactly one passing test per name
filter. Previously, a renamed or un-ignored assertion matched nothing
and passed silently.
- The 32-character demo-name rejection check is unchanged.

The full-suite reruns in the internal and demo states are kept on
purpose. They are the only coverage that the whole suite holds up in
those two shipped build shapes.

Estimate: the compiled-flag work goes from about 17 min to about 11.

### 2. Split Desktop Core into parallel, path-gated lanes
(`_ci-desktop.yml`)

- **Desktop JS:** `desktop-check`, `desktop-test` and `desktop-build`.
These compile no Rust, but some node:test cases read relay and DB crate
sources to pin shared constants (for example
`relayReconnectReplay.test.mjs`). So the job runs on desktop *and* Rust
changes, in parallel with the Tauri lanes. `lefthook.yml` notes this as
a deliberate local deviation.
- **Desktop Tauri (core | mesh | compiled-flags):** a matrix of parallel
Rust lanes.
- `core` and `compiled-flags` share the existing `desktop-core` Rust
cache key, so they start warm. `compiled-flags` restores it read-only.
- `mesh` keeps its own cache because `mesh-llm` pulls a different
dependency graph.
- **Smoke E2E and the Windows frontend build** compile no Rust and read
no crate sources, so they no longer run for Rust-only changes.
- **Smoke E2E goes from 4 to 10 shards.** Playwright shards by test
count, not duration. A simulation from the per-test durations in run
37635224099 reproduces the observed 4-shard split exactly. With 10
shards, the slowest shard runs about 11 min of tests.
- **The `Desktop` gate is stricter.** Each selected job must succeed and
each unselected job must be skipped, so a mis-gated job can't pass
silently. The required check context (`Desktop`) is unchanged.
`scripts/ci-required-gates.test.mjs` pins each job's `if:` to the gate's
selection expression, and checks which jobs a Rust-only, desktop-only,
Tauri, push, and empty selection pick.
- **Path-filter fixes:**
- The `desktop` filter now includes `_ci-desktop.yml`, `ci.yml` and
`Justfile` (which holds the desktop recipes), so edits to them run the
frontend lanes.
- The `rust` filter now matches `Justfile`. It still named the
pre-rename `justfile`, so a `Justfile`-only change selected no Rust
suites.
- `scripts/ci-selection.test.mjs` gains `Justfile` and desktop-workflow
scenarios, and the shared-workflow scenario now expects `desktop`.
- **Dead step removed:** the failure-only Playwright artifact upload in
the old Core job never had anything to upload, because that job never
ran Playwright.

### 3. Build relay artifacts in parallel (`_ci-relay.yml`)

- **The producer is now a 3-way matrix** (`relay-binaries`,
`backend-integration-tests`, `postgres-tests`).
- Each lane has its own exact-source cache entry and uploads
`desktop-e2e-relay-<artifact>`.
- Consumers download `desktop-e2e-relay-*` into `target/ci`, so their
paths are unchanged.
- The required `Desktop E2E Relay` context still reads the producer
job's aggregate result.
- **Rust cache saving:** all lanes restore the existing Rust cache key,
but only the widest lane (`postgres-tests`) saves it. Otherwise the
fastest lane could overwrite it with a narrower target dir.
- **Desktop E2E Integration goes from 2 to 3 shards.** Shard labels now
use `strategy.job-total`.

### 4. Bound degraded apt steps (`scripts/ci-apt-retry.sh`)

- With more shards, more runs hit the occasional degraded Ubuntu mirror.
On this PR, a Tauri lane ran `apt-get install` for 27 minutes: apt's
`Acquire` timeouts kept firing, but apt kept re-queuing the requests and
never failed. Separately, three Smoke shards stalled silently in
`playwright install-deps` (no output after `InRelease`) until the job
timeout. Healthy apt steps across four recent runs finished in at most
238s.
- Every apt-backed step in Desktop and Integration now runs through
`scripts/ci-apt-retry.sh`. The script writes the apt options to
`apt.conf.d`, so Playwright's own apt-get calls get them too. It kills
each attempt after 7 minutes (90s for `apt-get update`). Between
attempts it stops any `apt-get` or `dpkg` the attempt left running,
repairs dpkg under its own 60s deadline, and retries up to 3 times. The
stop matters for `playwright install-deps`, which runs `sudo sh -c
"apt-get update && apt-get install ..."`: sudo puts its command in a new
process group, so the deadline's signal stops `sh` and apt-get survives
holding the dpkg lock (seen on Smoke shard 8 of run 37696815557, and
reproduced with real sudo).
- Downloaded `.deb`s are kept between attempts, so a retry resumes where
the last one stopped. Against a mirror that stays degraded, this bounds
each wrapped command at about 25 minutes rather than recovering it. The
Tauri lanes wrap two commands, `apt-get update` (about 8.5 minutes worst
case) and `apt-get install` (about 25), so about 34 minutes together.
Job timeouts are sized to fit that bound plus the job's own work: Tauri
55m (lanes take up to ~15m), Integration 40m, and Smoke 45m. A degraded
mirror therefore ends with the wrapper's error instead of a silent job
timeout.
- **The retry has already fired on this PR.** In [run
37703795342](https://github.com/block/buzz/actions/runs/37703795342),
`playwright install-deps` on Integration shard 1/3 hit the 420s attempt
deadline. The second attempt started about 1.4s later, downloaded and
configured the real packages, and succeeded. The step took 526s (8m46),
and that shard took 17m24 while the other two took about 5m. Healthy
installs have taken at most 238s, so 420s leaves headroom, and a slow
mirror costs one attempt instead of the job.
- Between attempts the script stops **every** `apt-get`/`dpkg` on the
machine, not only the ones it started. That's intentional: on a hosted
runner any other one would hold the same dpkg lock. It assumes an
ephemeral runner, and the script says not to use it on a self-hosted
runner or a developer machine.
- `scripts/ci-apt-retry.test.mjs` covers the following with a fake
`sudo`: success, retry, the attempt budget, a stalled attempt, a stalled
dpkg repair, an apt-get that escapes the attempt's process group (on a
retry and on the final attempt), and usage. It needs Linux (GNU
`timeout`, `flock`, `setsid`, procps), so it skips on other platforms.
CI runs it on Ubuntu.

### What got simpler

- **Compiled-flag recipe:** two full-suite runs instead of three, six
cargo invocations instead of eight, and sidecar stubs no longer
invalidate the desktop build cache.
- **Path selection:** each desktop job declares only the paths that
actually affect it. The stale `justfile` filter and a dead artifact step
are gone.
- **Apt options:** set once in `apt.conf.d` by one script, instead of as
repeated `-o Acquire...` flags on each apt call.
- **Shard counts:** the shard count is written once per matrix, not
repeated in names and commands.

### Cost

- **More runners:** a full run uses more runner jobs. Smoke E2E goes
from 4 to 10 jobs, Desktop Core from 1 to 4, the relay producer from 1
to 3, and Integration from 2 to 3.
- **Fewer runners on single-area PRs:** desktop-only PRs skip the Rust
lanes, and Rust-only PRs skip Smoke E2E and the Windows build.
- **One extra Rust cache entry:** `desktop-mesh`.

### Related issue

None found.

### Testing

Blox, compiled-flag recipe at `77b9874b`:
- [x] Recipe passes with output redirected to a file. The log keeps all
4 state headers, the ignored assertions ran 2/2/2/3, and both full
suites passed (`3423 passed`).
- [x] A second back-to-back run shows no clean-state `Compiling
buzz-desktop`.
- [x] Mutation tests all fail as required:
  - `build.rs` auto-connect reads the owner-only var: rc=101.
  - The reverse swap: rc=101.
  - Rename `compiled_policy_matches_expected`: rc=1.
  - Wrong owner-only expectation: rc=101.
- [ ] `just ci`

Workflows:
- [x] `actionlint` on `_ci-desktop.yml`, `_ci-relay.yml` and `ci.yml`:
clean.
- [x] `scripts/test-ci-required-context-isolation.sh`: passes.
- [x] GitHub Actions: runs
[37701003713](https://github.com/block/buzz/actions/runs/37701003713)
and
[37703795342](https://github.com/block/buzz/actions/runs/37703795342)
took 27m09 and 28m51. Before this PR, PR runs had a median of 40.0m
(n=21) and main pushes took about 42m. These are observations across
mixed runner images, not a measured causal speedup.
- [x] Selection, gate and apt suites (74/74 on Linux), `actionlint` and
`bash -n` on Blox at tree `db9725fe`.

---------

Signed-off-by: Elrond <28d6302a099e5225b02c4155ac4236e4912603df2ab08dbfc2f4fef08ce598c8@buzz.block.builderlab.xyz>
Co-authored-by: Elrond <28d6302a099e5225b02c4155ac4236e4912603df2ab08dbfc2f4fef08ce598c8@buzz.block.builderlab.xyz>

scripts/ci-selection.test.mjs

@@ -222,7 +222,18 @@ const scenarios = [
   ["Tauri", ["desktop/src-tauri/src/main.rs"], ["desktop", "desktop-rust"]],
   ["relay", ["crates/buzz-relay/src/main.rs"], ["rust"]],
   ["migration", ["migrations/123.sql"], ["rust"]],
-  ["shared workflow", [".github/workflows/ci.yml"], ["rust", "mobile"]],
+  [
+    "shared workflow",
+    [".github/workflows/ci.yml"],
+    ["desktop", "mobile", "rust"],
+  ],
+  [
+    "desktop workflow",
+    [".github/workflows/_ci-desktop.yml"],
+    ["desktop", "mobile", "rust"],
+  ],
+  ["Justfile", ["Justfile"], ["desktop", "rust"]],
+  ["CI apt retry", ["scripts/ci-apt-retry.sh"], ["desktop", "rust"]],
   ["integration services", ["docker-compose.yml"], ["rust"]],
   ["CI integration images", ["docker-compose.ci.yml"], ["rust"]],
   [