hive-c0re: accept friendly MemoryMax size spellings, normalize for systemd

mara hit this directly: setting an agent's memory cap to "16GB"
fails with 'invalid MemoryMax "16GB": expected a size such as
"8G"...'. Confirmed directly against a running systemd 260
(systemd-run -p MemoryMax=<value>): systemd's own parser accepts a
bare byte count, <digits>B, or <digits> plus exactly one uppercase
K/M/G/T, and rejects both "16GB" (redundant B after a multiplier)
and "16g" (lowercase) with "Invalid argument". So the prior
rejection of "16GB" matched systemd, but is bad UX for input a
human reasonably expects to work.

validate_memory_max now returns the value to store (not just an
ok/err verdict): it accepts 8gb/8Gb/8GB/8g/8G interchangeably and
normalizes all of them to systemd's own 8G form before it is ever
persisted or passed downstream. Also fixes the adjacent bug the same
investigation turned up: the old validator incorrectly accepted
lowercase (8g) even though systemd itself rejects it.

Updated both call sites (server.rs, dashboard/lifecycle_ops.rs) to
use the normalized return value. New test
friendly_size_spellings_normalize_to_systemds_own_form; flipped the
old "8GB should be rejected" assertion, which encoded the
human-hostile behavior this fixes.

hive-c0re/src/agent_config/resource_limits.rs

@@ -260,18 +260,32 @@ pub fn validate_cpu_quota(value: &str) -> Result<(), String> {
     ))
 }
 
-/// Validate a systemd `MemoryMax=` value: a byte count with an optional
-/// `K`/`M`/`G`/`T` suffix, a percentage of physical memory, or the
-/// literal `infinity`.
+/// Validate a systemd `MemoryMax=` value — a byte count with an optional
+/// `K`/`M`/`G`/`T` suffix, a percentage of physical memory, or the literal
+/// `infinity` — and return the exact string to store and pass to systemd.
+///
+/// That's not always `value` itself: a size is accepted case-insensitively
+/// and with an optional redundant trailing `B` (`8gb`, `8Gb`, `8GB`, `8g`,
+/// `8G` are all the same size to a human), but only `8G` is what systemd's
+/// own parser actually takes — confirmed directly against a running
+/// systemd 260: `MemoryMax=8GB` and `MemoryMax=8g` both fail unit
+/// activation with "Invalid argument", while `MemoryMax=8G` starts fine.
+/// Accepting the friendly spellings and normalizing them here means every
+/// caller downstream only ever sees the one form systemd accepts, instead
+/// of everyone re-deriving that systemd is this particular about case and
+/// the redundant `B`.
 ///
 /// # Errors
 ///
 /// Returns a human-readable message naming the offending value and the
 /// three accepted shapes. Same operator-facing contract as
 /// [`validate_cpu_quota`].
-pub fn validate_memory_max(value: &str) -> Result<(), String> {
-    if value == "infinity" || is_percentage(value) || is_byte_size(value) {
-        return Ok(());
+pub fn validate_memory_max(value: &str) -> Result<String, String> {
+    if value == "infinity" || is_percentage(value) {
+        return Ok(value.to_owned());
+    }
+    if let Some(normalized) = normalized_byte_size(value) {
+        return Ok(normalized);
     }
     Err(format!(
         "invalid MemoryMax {value:?}: expected a size such as \"8G\", a percentage \
@@ -284,12 +298,32 @@ fn is_percentage(value: &str) -> bool {
     value.strip_suffix('%').is_some_and(is_plain_number)
 }
 
-/// A decimal number with an optional single-letter binary suffix.
-fn is_byte_size(value: &str) -> bool {
-    let mantissa = value
-        .strip_suffix(['K', 'M', 'G', 'T', 'k', 'm', 'g', 't'])
-        .unwrap_or(value);
-    is_plain_number(mantissa)
+/// A decimal number with an optional `K`/`M`/`G`/`T` suffix — accepted
+/// case-insensitively and with an optional trailing `B` (`gb`/`Gb`/`GB`/`g`
+/// are all read as `G`) — returned in the single uppercase-letter-no-
+/// redundant-`B` form systemd itself accepts. See [`validate_memory_max`]
+/// for why. A trailing `B` with no multiplier before it (`1048576B`) is a
+/// bare byte count and kept as-is — systemd accepts `B` as a unit on its
+/// own, unlike the redundant `KB`/`MB`/`GB`/`TB` combinations.
+fn normalized_byte_size(value: &str) -> Option<String> {
+    if let Some(before_b) = value.strip_suffix(['B', 'b']) {
+        return match before_b.strip_suffix(['K', 'M', 'G', 'T', 'k', 'm', 'g', 't']) {
+            Some(mantissa) if is_plain_number(mantissa) => {
+                let unit = before_b[mantissa.len()..].to_ascii_uppercase();
+                Some(format!("{mantissa}{unit}"))
+            }
+            Some(_) => None,
+            None => is_plain_number(before_b).then(|| format!("{before_b}B")),
+        };
+    }
+    match value.strip_suffix(['K', 'M', 'G', 'T', 'k', 'm', 'g', 't']) {
+        Some(mantissa) if is_plain_number(mantissa) => {
+            let unit = value[mantissa.len()..].to_ascii_uppercase();
+            Some(format!("{mantissa}{unit}"))
+        }
+        Some(_) => None,
+        None => is_plain_number(value).then(|| value.to_owned()),
+    }
 }
 
 /// Digits, optionally followed by a single `.` and more digits. Hand
@@ -402,9 +436,31 @@ mod tests {
         }
     }
 
+    /// mara hit this directly: "16GB" reads as an obviously
+    /// valid size to a human, but systemd's own parser takes only the
+    /// single-letter form — confirmed against a running systemd 260,
+    /// `MemoryMax=16GB` and `MemoryMax=16g` both fail unit activation,
+    /// `MemoryMax=16G` doesn't. Accept the friendly spellings and normalize
+    /// them to what systemd actually wants, rather than rejecting input a
+    /// human reasonably expects to work.
+    #[test]
+    fn friendly_size_spellings_normalize_to_systemds_own_form() {
+        for (input, want) in [
+            ("8GB", "8G"),
+            ("8Gb", "8G"),
+            ("8gb", "8G"),
+            ("8g", "8G"),
+            ("512mb", "512M"),
+            ("1048576b", "1048576B"),
+            ("1.5gb", "1.5G"),
+        ] {
+            assert_eq!(validate_memory_max(input).as_deref(), Ok(want));
+        }
+    }
+
     #[test]
     fn rejects_invalid_memory_maxes() {
-        for v in ["", "8GB", "G", "abc", "-8G", "8 G", "Infinity", "8Gi"] {
+        for v in ["", "G", "abc", "-8G", "8 G", "Infinity", "8Gi", "8KG"] {
             assert!(validate_memory_max(v).is_err(), "{v} should be rejected");
         }
     }