feat(p6-stop): --stop-after/--stop-at deadline transfer stop

src/shared/stop_condition.h

@@ -0,0 +1,46 @@
+#ifndef STOP_CONDITION_H
+#define STOP_CONDITION_H
+
+#include <stdbool.h>
+#include <time.h>
+
+/* Client-only transfer stop conditions (--stop-after=MINS / --stop-at=TIME).
+ * Both are local sender-side deadlines: they are never serialized into the
+ * config frame and never bump PROTOCOL_VERSION.  A transfer checks the
+ * condition at natural chunk/file boundaries and, once reached, stops
+ * elegantly (everything already sent is finalized normally, exit 0).
+ *
+ * A condition combines an optional CLOCK_MONOTONIC instant (the relative
+ * --stop-after duration, immune to wall-clock changes) with an optional
+ * wall-clock instant (the absolute --stop-at form).  Either one being reached
+ * ends the transfer. */
+typedef struct StopCondition {
+  bool has_monotonic;
+  struct timespec monotonic_deadline;
+  bool has_wall;
+  time_t wall_deadline;
+} StopCondition;
+
+/* Parse --stop-after=MINS: a positive integer count of minutes.  Zero,
+ * negative, empty and non-numeric values are rejected.  Returns true when
+ * accepted and stores the value in *out_minutes. */
+bool stop_parse_after_minutes(const char* value, int* out_minutes);
+
+/* Parse --stop-at=TIME.  Accepted forms are HH:MM, HH:MM:SS and
+ * now+N[smhd] (seconds/minutes/hours/days from now).  The absolute forms are
+ * resolved against `now` (local wall clock) and written to *out_deadline; a
+ * time already in the past yields a deadline <= now ("stop immediately").
+ * Returns false on any malformed value. */
+bool stop_parse_at_time(const char* value, time_t now, time_t* out_deadline);
+
+/* Build the runtime condition at transfer start.  after_minutes is the
+ * relative --stop-after duration (<= 0 disables it); at_time is the absolute
+ * --stop-at deadline (only consulted when has_at is true); now_mono is the
+ * CLOCK_MONOTONIC reading at start. */
+StopCondition stop_condition_make(bool has_after, int after_minutes, bool has_at, time_t at_time,
+                                  struct timespec now_mono);
+
+/* True once either deadline has passed (wall clock first, then monotonic). */
+bool stop_condition_reached(const StopCondition* condition);
+
+#endif