perf(console): extend the filtered view incrementally

With any console filter on, each batch of new output rescanned all N
lines to rebuild the visible set. A text filter lowercase-copied the
needle and every line to test it: O(total characters) and 2N
allocations per batch.

When the filter is unchanged and the model only appended or evicted
lines since the last pass, the visible indices drop the evicted lines
and shift down, and only the new lines are tested. The result equals
a full rescan, since line text and channel never change and the
filtered view has no folds. A filter change, Clear, or a model window
that doesn't follow on from the last one still rescans.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/test_phase4.cpp

@@ -5858,6 +5858,35 @@ void testConsoleWrapCache()
     }
 }
 
+// ExtendFlatVisibleIndices (console_output_model.h): the incremental filtered visible set equals a full rescan.
+void testConsoleFlatVisibleIndices()
+{
+    using dragonx::ui::ExtendFlatVisibleIndices;
+    std::deque<std::string> mdl;
+    std::uint64_t first = 0;
+    auto passes = [&mdl](int i) { return mdl[static_cast<std::size_t>(i)].find('x') != std::string::npos; };
+    auto rescan = [&]() {
+        std::vector<int> v;
+        for (int i = 0; i < static_cast<int>(mdl.size()); ++i) if (passes(i)) v.push_back(i);
+        return v;
+    };
+    for (int i = 0; i < 20; ++i) mdl.push_back(i % 3 == 0 ? "x" + std::to_string(i) : std::string("y"));
+    std::vector<int> vis = rescan();
+    std::uint64_t oldFirst = first, oldEnd = first + mdl.size();
+    for (int k = 0; k < 4; ++k) { mdl.pop_front(); ++first; }                 // evict 4 (incl. matches 0 and 3)
+    for (int i = 20; i < 25; ++i) mdl.push_back(i % 2 == 0 ? "x" : "y");      // append 5
+    EXPECT_TRUE(ExtendFlatVisibleIndices(vis, oldFirst, oldEnd, first, static_cast<int>(mdl.size()), passes));
+    EXPECT_TRUE(vis == rescan());
+    const std::vector<int> untouched = vis;                                   // non-chaining window => refused
+    EXPECT_FALSE(ExtendFlatVisibleIndices(vis, first, first + mdl.size(), first + mdl.size() + 1, 3, passes));
+    EXPECT_TRUE(vis == untouched);
+    oldFirst = first; oldEnd = first + mdl.size();                           // clear(): firstSeq jumps to old end
+    first += mdl.size();
+    mdl.clear(); mdl.push_back("x"); mdl.push_back("y");
+    EXPECT_TRUE(ExtendFlatVisibleIndices(vis, oldFirst, oldEnd, first, static_cast<int>(mdl.size()), passes));
+    EXPECT_TRUE(vis == rescan());
+}
+
 // ConsoleScrollController — auto-scroll state machine (pin, wheel-up cooldown, backlog).
 void testConsoleScrollController()
 {
@@ -15098,6 +15127,7 @@ int main()
     testDaemonLifecycleAdapters();
     testConsoleTextLayout();
     testConsoleWrapCache();
+    testConsoleFlatVisibleIndices();
     testConsoleModel();
     testPortfolioHelpers();
     testMarketSeries();