Close the guard's blind spot: named short timeouts

A fifth flake landed on CI while the first guard was in review —
GossipSyncBoardTests timing out at 1.03s — and the guard did not catch it,
because the deadline was `TestConstants.shortTimeout` rather than a
literal. A literals-only scan cannot see a short value behind a symbol,
which is the more common way it is written: 81 wait sites used
shortTimeout (1s) or defaultTimeout (5s), every one of them below the
floor.

Rather than guess which of those were safe to raise, all 81 were converted
and the suite timed. Runtime went 15s -> 72s, which located the genuine
negative waits precisely: ten tests that assert something does *not*
happen and therefore always run their deadline out. Measurement instead of
a heuristic, since a mis-guess in either direction is invisible — too
short reintroduces the flake, too long silently costs a minute a run.

Those 28 sites now use `TestConstants.negativeWaitWindow`, a named
constant whose doc explains the inverted reasoning: for a negative wait,
starvation can only make the assertion *more* likely to hold, so short is
correct, and the name states the polarity instead of leaving a bare
literal that reads like the mistake. Suite is back to 15.3s.

The guard now also rejects `timeout: TestConstants.shortTimeout` and
`defaultTimeout`, while accepting `negativeWaitWindow` by name.

Re-verified with a canary carrying every banned shape — literal default,
both named constants, and an elapsed-time upper bound. All four were
flagged with file and line; the suite went green again on removal.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

bitchatTests/ChatViewModelRefactoringTests.swift

@@ -43,14 +43,14 @@ struct ChatViewModelRefactoringTests {
         transport.simulateConnect(peerID, nickname: "alice")
 
         let didResolve = await TestHelpers.waitUntil({ viewModel.getPeerIDForNickname("alice") != nil },
-                                                     timeout: TestConstants.shortTimeout)
+                                                     timeout: TestConstants.settleTimeout)
         #expect(didResolve)
         
         // Action: User types /msg command
         viewModel.sendMessage("/msg @alice Hello Private World")
 
         let didSend = await TestHelpers.waitUntil({ transport.sentPrivateMessages.count == 1 },
-                                                  timeout: TestConstants.shortTimeout)
+                                                  timeout: TestConstants.settleTimeout)
         #expect(didSend)
         
         // Assert:
@@ -74,7 +74,7 @@ struct ChatViewModelRefactoringTests {
         transport.simulateConnect(peerID, nickname: "troll")
 
         let didResolve = await TestHelpers.waitUntil({ viewModel.getPeerIDForNickname("troll") != nil },
-                                                     timeout: TestConstants.shortTimeout)
+                                                     timeout: TestConstants.settleTimeout)
         #expect(didResolve)
         
         // Action
@@ -83,7 +83,7 @@ struct ChatViewModelRefactoringTests {
         // Assert
         // Verify identity manager was called to block "fingerprint_123"
         let didBlock = await TestHelpers.waitUntil({ identity.isBlocked(fingerprint: "fingerprint_123") },
-                                                   timeout: TestConstants.shortTimeout)
+                                                   timeout: TestConstants.settleTimeout)
         #expect(didBlock)
     }
 
@@ -114,7 +114,7 @@ struct ChatViewModelRefactoringTests {
         // Wait for async processing with proper timeout
         let found = await TestHelpers.waitUntil(
             { viewModel.privateChats[senderID]?.first?.content == "Secret" },
-            timeout: TestConstants.defaultTimeout
+            timeout: TestConstants.settleTimeout
         )
 
         // Assert
@@ -140,7 +140,7 @@ struct ChatViewModelRefactoringTests {
             {
                 viewModel.publicMessages(for: .mesh).contains(where: { $0.content == "Public Hi" })
             },
-            timeout: TestConstants.defaultTimeout
+            timeout: TestConstants.settleTimeout
         )
 
         // Assert