§5 3.2 reproduces on glass and the shipped fix is not sufficient: the panel stays dark after
teardown. Two candidates were left undistinguished by the first on-glass run — the adopted snapshot
was already poisoned, or the dark-desk backstop never fired — because the case had no way to tell
them apart. This adds that way.
**The subscriber.** The adoption arm and `restore_displays_ccd`'s backstop announce themselves ONLY
through `tracing`, and a bare `cargo test` harness installs no subscriber, so both events went
nowhere. `tracing-subscriber` becomes a DEV-dependency of pf-vdisplay (the shipped host's closure
through this crate is unchanged) and `init_test_tracing` wires it: `try_init` so a second live case
in the same binary is a no-op rather than a panic, `with_test_writer` so it interleaves with the
harness rather than racing `println!`, `RUST_LOG` still winning over the `debug` default.
`live_inplace_resize` gets it too — its comment claimed tracing-subscriber "is not a dep of this
crate, run the host binary for traced runs", which was the same blindness written down as a
limitation. It no longer holds.
**The probe is the actual discriminator, and it needs no logs at all.** Member 1's isolate is
INJECTED to fail, so nothing of ours deactivates anything there. Sampling `active_physicals()`
immediately after member 1's create therefore answers the question directly:
* empty -> the arriving IddCx monitor took the desktop on its own. Every snapshot from that instant
on records "panel off", so member 2's adopted snapshot is POISONED AT BIRTH and restoring it
faithfully restores darkness. Adoption works; the snapshot SOURCE is the defect.
* non-empty -> poisoning is excluded and the break is downstream: no adoption line means teardown's
restore was never gated on, a backstop line with a non-zero force-EXTEND rc means the remedy
itself failed.
The failing assertion now reads that verdict out instead of asserting one cause, so the next on-glass
run reports which link broke rather than only that one did.
⚠️ Still UNRUN on glass — this is the instrument, not the measurement. Needs .173's CONSOLE session
(ssh is session 0 and CCD sees nothing there), and it can leave the desk dark: recover with
`SDC_USE_DATABASE_CURRENT|SDC_APPLY`, not EXTEND, which returns rc=31 against a single display.
Checked while writing this, and recorded so it is not re-derived: the "backstop is structurally
inert on a one-display box" theory does NOT survive. Both real call sites restore BEFORE the virtual
is REMOVEd, so two displays are connected and the preset applies — `live_force_extend_*` measured
exactly that (1 -> 1 -> 2). The documented residual is narrower: a restore that fails once the
virtual is already gone.
Verified: `xcheck.sh windows clippy` clean (it passes `--all-targets`, so this test code really is
compiled), `cargo fmt --all --check` clean.
⚠️ `Cargo.lock` moves with this commit and must not be split from it. CI runs
`cargo clippy --workspace --all-targets --locked`, so a new dependency edge whose lockfile entry is
missing does not degrade to a re-resolve — it FAILS the build outright. The dev-dependency adds one
line (pf-vdisplay gains a `tracing-subscriber` edge; the package itself was already in the graph via
punktfunk-host and pf-encode, so nothing new is vendored).
enricobuehler
ed021a13ee