test: state-machine tests for watchVideoTrackForRemoval

15 unit + integration tests that extract the function and the shipped
VIDEO_REMOVE_MUTE_WINDOW_MS constant from web/zebra-spaces.html so the
assertions track exactly what's deployed. Drives synthetic mute/
unmute/ended event sequences against a fake EventTarget track with a
fake clock injected through a Function-constructor harness.

Unit coverage:
- shipped window must be >= 10s (catches accidental shorten)
- initial mute (never flowed) never removes
- flowing + sustained mute past window removes
- mute + unmute within window cancels removal
- ended event removes immediately + cancels pending timer
- removeFn is idempotent (no double-call across mute, ended, or later
  events)
- redundant mute events do not stack timers
- rescue and removal both emit logLine telemetry
- rapid mute/unmute oscillation never removes while unmute lands in time

Integration coverage (realistic lifecycles):
- fresh track -> flow -> publisher unshares -> tile removed
- mobile network handoff (long mute) recovers without removal
- peer leaves abruptly (ended fires) -> tile removed once
- hard refresh of publisher (SFU supplant renegotiation gap) -> tile
  survives — this is the cascade fox flagged where a phone reconnect
  was killing the host's view of its camera
- publisher process crashes (mute holds indefinitely) -> removed at
  window

Wired into Makefile as test-video-removal + added to test-all. Pure
Node, no browser or proxy server needed.

Makefile

@@ -25,6 +25,15 @@ test-web:
 test-fsm:
 	@node test/zebra-fsm.test.js
 
+# Receive-side stream lifecycle (watchVideoTrackForRemoval) — fake-clock
+# state-machine tests covering 'when is it safe to remove a tile'. Catches
+# the regressions where transient mutes (NACK gaps, network blips, mobile
+# handoffs, hard-refresh renegotiation churn) would otherwise kill live
+# tiles. Extracts the function from the page and the shipped mute window
+# so the assertions track what's live.
+test-video-removal:
+	@node test/video-track-removal.test.js
+
 # zebra-spaces JS↔Go protocol parity + vault + ed25519 + (optionally) a live
 # server flow. The live-server tier auto-runs when proxy.unturf.com sits
 # alongside this checkout AND has a Go toolchain — we build the relay binary
@@ -42,7 +51,7 @@ test-zebra-spaces:
 	ZEBRA_SPACES_BINARY=$$bin node test/zebra-spaces.test.js; \
 	rc=$$?; rm -f /tmp/zspc-signal-test; exit $$rc
 
-test-all: test/unit test/integration test/functional test-web test-fsm test-zebra-spaces
+test-all: test/unit test/integration test/functional test-web test-fsm test-video-removal test-zebra-spaces
 	@echo "--- unit ---"
 	@./test/unit
 	@echo "--- integration ---"
@@ -53,6 +62,8 @@ test-all: test/unit test/integration test/functional test-web test-fsm test-zebr
 	@node test/web-protocol.test.js
 	@echo "--- zebra-fsm ---"
 	@node test/zebra-fsm.test.js
+	@echo "--- video-track-removal ---"
+	@node test/video-track-removal.test.js
 	@echo "--- zebra-spaces ---"
 	@$(MAKE) -s test-zebra-spaces