feat(registry): commands, watches, samples, the timeline and conditions

The app side of Crafter.Debug, minus the session:

- Command(name, description, handler): the handler takes nothing or
  one argument struct and returns void, a value, Result<T> or
  Async<T>. Arguments are decoded before it runs, so a mistyped call
  is answered with every mistake and never reaches it; a throwing
  handler becomes an Exception error instead of unwinding into the
  frame loop. This replaces 3DForts' three-file pattern per verb.
- Watch(path, variable | getter [, setter]) with bounds, help and
  read-only, and Sample(path, value) from any thread with a
  frame-stamped history. Paths resolve into values ("bodies[1].pos.y")
  and set the same way, writing a member writes the whole value back.
  Unknown paths and commands get a suggestion.
- Group: registrations under a prefix that end with their owner. Not
  movable, so neither is its owner: its watches refer to the owner's
  members, and a move would leave them pointing at the old object.
- Log, LogWarn, LogError, Check and Emit on one frame-stamped
  timeline, with source locations captured without macros. A check
  failing every frame is counted every time but stored sparsely, and
  the session's listener hears every failure.
- Condition: what `wait` and `pause --when` evaluate each frame. A
  condition that cannot be decided reports why instead of being false,
  which would make a wait hang.

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

project.cpp

@@ -27,12 +27,21 @@ namespace {
         return fs::path(std::source_location::current().file_name()).parent_path();
     }
 
-    constexpr std::array<std::string_view, 4> tests = {
+    // Tests of the core, linked against it alone.
+    constexpr std::array<std::string_view, 4> coreTests = {
         "ShouldRoundTripJson",
         "ShouldRoundTripAggregates",
         "ShouldReportDecodeErrorsWithPaths",
         "ShouldDescribeDefaultsAndRequired",
     };
+
+    // Tests of the app library.
+    constexpr std::array<std::string_view, 4> libraryTests = {
+        "ShouldInvokeCommands",
+        "ShouldResolveWatchPaths",
+        "ShouldRecordTimeline",
+        "ShouldEvaluateConditions",
+    };
 }
 
 extern "C" Configuration CrafterBuildProject(std::span<const std::string_view> args) {
@@ -85,15 +94,25 @@ extern "C" Configuration CrafterBuildProject(std::span<const std::string_view> a
 
     cfg.dependencies = { &core, &client };
     {
-        std::array<fs::path, 1> interfaces = { "interfaces/Crafter.Debug" };
-        std::array<fs::path, 0> implementations = {};
+        std::array<fs::path, 4> interfaces = {
+            "interfaces/Crafter.Debug-Registry",
+            "interfaces/Crafter.Debug-Timeline",
+            "interfaces/Crafter.Debug-Condition",
+            "interfaces/Crafter.Debug",
+        };
+        std::array<fs::path, 3> implementations = {
+            "implementations/Crafter.Debug-Registry",
+            "implementations/Crafter.Debug-Timeline",
+            "implementations/Crafter.Debug-Condition",
+        };
         cfg.GetInterfacesAndImplementations(interfaces, implementations);
     }
 
     // Tests only when this is the project being built: a consumer's load of
     // this file has no use for them.
     if (IsTopLevelProject()) {
-        for (const std::string_view test : tests) cfg.AddTest(test).Dependencies({ &core });
+        for (const std::string_view test : coreTests) cfg.AddTest(test).Dependencies({ &core });
+        for (const std::string_view test : libraryTests) cfg.AddTest(test).Dependencies({ &cfg });
     }
     return cfg;
 }