Fix decode-screen NPE crash when a message has a null destination call

[patrickrb]

Root cause

Ft8Message.checkIsCQ() dereferenced callsignTo before its guard, and the guard checked the wrong variable:

String s = callsignTo.trim().split(" ")[0];   // NPE here when callsignTo == null
if (s == null) { return false; }              // dead: String.split()[0] is never null

callsignTo defaults to null (public String callsignTo = null) and stays null for free-text/telemetry frames and unresolved-hash decodes that still reach the published decode list. The if (s == null) check is dead — String.split()[0] never returns null — so the intended "missing destination → not a CQ" behaviour never actually protected the real deref.

Impact (live main-thread crash on the primary screen)

The Compose decode screen calls checkIsCQ() unconditionally on the main thread with no try/catch:

• DecodeRow.kt:72 — for every rendered decode row
• DecodeRow.kt:352 — inside resolveQsoStatus(...)
• DecodeScreen.kt:479, 511, 515 — inside filterMessages(...) ("Show only CQ", "CQ Calls", "New DXCC")

A single decode with a null callsignTo therefore crashed the whole app on the app's primary screen.

This is proven reachable by the existing #254 guard already present in ActiveQsoPanel.kt:104:

// Guard: checkIsCQ() calls callsignTo.trim() which NPEs on null. (#254)
if (msg.callsignTo != null && msg.checkIsCQ()) return@forEach

ActiveQsoPanel is a sibling consumer of the same mainViewModel.mutableFt8MessageList. That guard was added there but not to the decode-list consumers, which have the identical deref.

Fix

Null-guard callsignTo inside checkIsCQ() itself — the single choke point every caller funnels through — so a missing destination returns "not a CQ" instead of throwing. This covers DecodeRow, resolveQsoStatus, filterMessages, and MapScreen at once. Behaviour is byte-for-byte unchanged for any message that has a callsignTo.

Testing performed

• Added Ft8MessageTest.checkIsCQ_falseWhenCallsignToNull — reproduces the NPE against the unfixed code (java.lang.NullPointerException), passes after the fix.
• :app:testDebugUnitTest — full unit suite green.
• :app:assembleDebug — clean APK build across all 4 ABIs.

Risk

Minimal. One-line defensive null-guard in a leaf helper; no protocol/DSP/threading behaviour changes; no change for well-formed messages.

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 36.62%. Comparing base (adf04bb) to head (8528cff).

Additional details and impacted files

@@            Coverage Diff            @@
##                dev     #609   +/-   ##
=========================================
  Coverage     36.62%   36.62%           
  Complexity      197      197           
=========================================
  Files           216      216           
  Lines         26885    26885           
  Branches       3294     3294           
=========================================
  Hits           9847     9847           
  Misses        16811    16811           
  Partials        227      227           

Flag	Coverage Δ
android	15.03% <ø> (ø)
native	9.93% <ø> (ø)

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[Copilot]

Pull request overview

This pull request fixes a crash in the decode UI path by making Ft8Message.checkIsCQ() null-safe when callsignTo is missing (which can occur for free-text/telemetry/unresolved-hash decodes that still reach the rendered decode list).

Changes:

• Add a defensive callsignTo == null guard inside Ft8Message.checkIsCQ() to return false instead of throwing.
• Add a unit test ensuring checkIsCQ() returns false (and does not NPE) when callsignTo is left at its default null.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
ft8af/app/src/main/java/com/k1af/ft8af/Ft8Message.java	Makes checkIsCQ() resilient to callsignTo == null, preventing main-thread crashes in UI callers.
ft8af/app/src/test/java/com/k1af/ft8af/Ft8MessageTest.java	Adds regression coverage for the null-destination case to prevent reintroducing the crash.

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