Document snapshot pointer lifetimes and make getters NULL-safe

The snapshot getters crashed on a NULL snapshot, unlike the rest of the
API. They now return NULL, an empty span, 0, or write nothing, as the
terminal functions do. term_snapshot_cluster writes nothing when cps is
NULL or cap is 0.

Document that the view and its palette keep their address for the life
of the snapshot, and that a row pointer lasts only until the next update
or free, since an update can realloc the cell array.

Rename the term_input.h include guard to TERM_INPUT_H to match the file.

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

1 files changed, 8 insertions, 6 deletions

diff --git a/src/snapshot.c b/src/snapshot.c
index 8dbb498..c578f18 100644
--- a/src/snapshot.c
+++ b/src/snapshot.c
@@ -314,34 +314,36 @@ bool term_snapshot_update(struct term_snapshot *s, struct term *t)
 
 const struct term_view *term_snapshot_view(const struct term_snapshot *s)
 {
-    return &s->view;
+    return s ? &s->view : NULL;
 }
 
 const struct term_cell *term_snapshot_row(const struct term_snapshot *s, int y)
 {
-    if (y < 0 || y >= s->view.size.y)
+    if (!s || y < 0 || y >= s->view.size.y)
         return NULL;
     return s->cells + (size_t)y * s->view.size.x;
 }
 
 uint64_t term_snapshot_row_key(const struct term_snapshot *s, int y)
 {
-    if (y < 0 || y >= s->view.size.y)
+    if (!s || y < 0 || y >= s->view.size.y)
         return 0;
     return s->keys[y];
 }
 
 struct term_span term_snapshot_row_selection(const struct term_snapshot *s, int y)
 {
-    if (y < 0 || y >= s->view.size.y)
+    if (!s || y < 0 || y >= s->view.size.y)
         return (struct term_span){ 0 };
     return s->selection[y];
 }
 
 int term_snapshot_cluster(const struct term_snapshot *s, uint32_t text, uint32_t *cps, int cap)
 {
+    if (!s)
+        return 0;
     if (!(text & TERM_TEXT_CLUSTER)) {
-        if (cap > 0)
+        if (cps && cap > 0)
             cps[0] = text;
         return 1;
     }
@@ -350,7 +352,7 @@ int term_snapshot_cluster(const struct term_snapshot *s, uint32_t text, uint32_t
         return 0;
     int n = (int)s->arena[off];
     int copy = n < cap ? n : cap;
-    if (copy > 0)
+    if (cps && copy > 0)
         memcpy(cps, &s->arena[off + 1], (size_t)copy * sizeof(*cps));
     return n;
 }