@spec age_days(DateTime.t(), DateTime.t()) :: non_neg_integer()

Returns the age in whole days since dt relative to now.

If dt is in the future, returns 0.

@spec age_line(Memory.t(), DateTime.t()) :: binary()

Returns an "Age" line for a memory.

Examples:

• "Age: unknown (missing timestamps)"
• "Age: 312 days (updated 12 days ago)"

Notes:

• Uses updated_at if present; otherwise uses inserted_at.
• Uses now for deterministic testing.

@spec parse_ts(nil | iso8601()) :: {:ok, DateTime.t()} | :error

Parse an ISO8601 timestamp string into a DateTime.

Returns {:ok, dt} or :error.

@spec warning_line(Memory.t(), DateTime.t(), keyword()) :: binary() | nil

Returns an optional warning line based on how long ago the memory was updated.

• If updated_at is missing/unparseable, returns nil.
• If updated_days >= strong_days, returns a strong warning.
• Else if updated_days >= mild_days, returns a mild warning.
• Else returns nil.

This is intended as a gentle prompt to check for cobwebs.