bake: name the five ways the extension can fail to answer, and move the landing verdict into a pure, tab-provable classifier

A no-answer stays a failure; it now says whether the extension never ran the landing, answered a stale generation, spoke a wire this build cannot read, cleared the request, or refused it.

src/core/wire/bake_wire.cpp

@@ -2,6 +2,8 @@
 
 #include "core/wire/bake_wire.h"
 
+#include <utility>
+
 #include "core/version/app_version.h"
 #include "core/wire/wire.h"
 
@@ -122,4 +124,49 @@ std::optional<BakeOutcome> decodeBakeOutcome(const std::string& wire) {
     return outcome;
 }
 
+BakeAnswer classifyBakeAnswer(const std::optional<std::string>& raw,
+                              const BakeRequest& sent) {
+    BakeAnswer answer;
+    if (!raw || raw->empty()) {
+        answer.kind = BakeAnswerKind::Cleared;
+        return answer;
+    }
+    if (std::optional<BakeOutcome> outcome = decodeBakeOutcome(*raw)) {
+        answer.kind = outcome->generation == sent.generation
+                          ? BakeAnswerKind::Answered
+                          : BakeAnswerKind::ForeignOutcome;
+        answer.outcome = std::move(outcome);
+        return answer;
+    }
+    // Still a request: whether it is OURS is what separates "nothing read this key" from
+    // "another instance overwrote it" — a persisted instanceGuid is copyable, so two
+    // instances CAN name one key.
+    if (const std::optional<BakeRequest> req = decodeBakeRequest(*raw)) {
+        answer.kind =
+            *req == sent ? BakeAnswerKind::Unanswered : BakeAnswerKind::ForeignRequest;
+        return answer;
+    }
+    answer.kind = BakeAnswerKind::Undecodable;
+    return answer;
+}
+
+BakeScanVerdict classifyBakeScan(const BakeScanContext& session, const BakeScanKey& key,
+                                 std::int64_t nowSec) {
+    // Not a request: an outcome the writing instance has not collected yet, or a value
+    // from a build we do not read. The writer owns clearing its own key.
+    if (!key.decoded) return BakeScanVerdict::Ignore;
+
+    // Either direction, so a clock moved backwards is caught too.
+    const std::int64_t age = nowSec - key.generation;
+    if (age > kMaxRequestAgeSeconds || age < -kMaxRequestAgeSeconds)
+        return BakeScanVerdict::ClearStale;
+
+    // Three tabs have to agree before anything may land: the tab the request was found in,
+    // the tab the session's book/ledger last loaded, and the tab a persist will write into.
+    // Landing on a disagreement writes one tab's bake into another's bank.
+    const bool landable = session.sessionHasLoadedProject &&
+                          session.loadedProjectIsActive && key.inLoadedProject;
+    return landable ? BakeScanVerdict::Land : BakeScanVerdict::RefuseWrongProject;
+}
+
 }  // namespace reasampler::wire