fix: what an audit of the documented behaviour found

An independent check of every behaviour AGENTS.md was to describe:
- `--units ,` and `--only ,` skipped their empty items and so had no
  filter left: a typo started a run of every unit. They are usage errors
  now (exit 3).
- Two fixes the plan lists were missing: a dry run now clears the prompts
  a dry run before it left in the dir they share (the report counted
  them), and `config` reports an absolute functional.mcp.command that is
  no program here - /usr/bin/npx inside the Flatpak, whose /usr is the
  Sdk's.
- A patch that is not UTF-8 stops `run` at preflight (exit 3), as the
  plan has it; it exited 1.
- An exception no command caught aborted the process (134), e.g. a home
  that holds no lenses: it ends with its message and exit 1. An error
  escaping `run` or `freeze` now also clears the signal handler's run and
  sweeps what is left below the subreaper.
- `config -h` printed "unrecognized arguments" (exit 3): it prints the
  usage, exit 0.
- An API seat's .claude.json is linked into place, so a second writer
  never replaces the first's file and what claude wrote to it since.

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

implementations/Crafter.Review-Run.cpp

@@ -390,6 +390,11 @@ namespace Crafter::Review::Run {
             built = Inventory::Build("commits", a.artifact);
         } catch (const Inventory::InvariantError& e) {
             Die(e.what());
+        } catch (const Dyn::Error& e) {
+            // A patch that is not UTF-8 is no artifact to review: a preflight
+            // failure.
+            if (e.Kind() != "UnicodeDecodeError") throw;
+            Die(std::format("the artifact's patches are not UTF-8 ({}) - re-freeze", e.what()));
         }
         units = built.out.at("units");
         lines = built.lines;
@@ -449,6 +454,12 @@ namespace Crafter::Review::Run {
         }
         scratch = scratchRoot / std::format("{}-run-{}{}", h8, runN, a.dryRun ? "-dry" : "");
         fs::create_directories(scratch);
+        if (a.dryRun) {
+            // Every dry run on a hash shares this dir: the report counts
+            // this run's prompts, not the last one's too.
+            std::error_code error;
+            fs::remove_all(scratch / "prompts", error);
+        }
         if (!a.dryRun) {
             // A stop meant for a run this dir held before is not this run's.
             std::error_code error;
@@ -2161,6 +2172,16 @@ namespace Crafter::Review::Run {
         Process::BecomeSubreaper();
         Run run(std::move(a), cfg);
         Current = &run;
+        // However this ends - a return, or an exception on its way to Main's
+        // handler - the signal handler loses its run, and whatever is left
+        // below this subreaper (a daemon a git call started) goes with it;
+        // never a process it did not start.
+        struct Cleanup {
+            ~Cleanup() {
+                Current = nullptr;
+                Process::KillDescendants();
+            }
+        } const cleanup;
         // `crafter-review stop`: the file is looked at every 2 s, and a stop
         // is handled exactly like SIGTERM.
         std::jthread watcher([&run](const std::stop_token& token) {
@@ -2189,10 +2210,6 @@ namespace Crafter::Review::Run {
         }
         watcher.request_stop();
         watcher.join();
-        Current = nullptr;
-        // Whatever is left below this subreaper - a daemon a git call
-        // started - goes with it; never a process it did not start.
-        Process::KillDescendants();
         return code;
     }
 }