docs: draft TUI polish companion spec

CONTEXT.md

@@ -32,13 +32,25 @@ _Avoid_: Data directory, history.jsonl, the database (generic)
 The condition where the observation store is present but cannot be read or trusted — unreadable, corrupt, or written by a newer Fenris — degrading every view that depends on it rather than crashing or guessing.
 _Avoid_: Database error, corruption, broken data
 
+**Usage interval**:
+The elapsed span between two compatible counter observations, with a measured usage total whose distribution within that span may be unknown.
+_Avoid_: Estimated hourly usage, interpolated sample
+
+**Unallocated usage**:
+Measured usage whose share in a particular hour, calendar day, or monitoring period cannot be established from the available evidence.
+_Avoid_: Zero usage, evenly distributed writes
+
 **Hour observation**:
-One row per UTC hour in the observation store, recording that hour's usage-habit split into active, idle, powered-off, and unknown seconds, plus write/read deltas, thermal evidence, and coverage.
+The usage-habit evidence for a UTC hour's represented elapsed span: active, idle, powered-off, and unknown time, measured usage, thermal evidence, and coverage. A partial hour does not describe future time.
 _Avoid_: Hourly record, hourly.jsonl entry
 
 **Day aggregate**:
-One row per UTC day derived from hour observations; the grain at which usage-habit evidence is judged.
-_Avoid_: Daily summary, daily stats
+The UTC-day summary at which usage-habit evidence is judged; distinct from a local display day.
+_Avoid_: Local daily total, daily stats
+
+**Local display day**:
+A calendar day in the user's current system timezone, used to browse observation history; its elapsed length can vary with timezone transitions.
+_Avoid_: UTC evidence day, fixed 24-hour day
 
 **Controller segment**:
 A span of observation history within which the drive's controller identity is unchanged and counters are monotonic; write deltas are never computed across a segment boundary.
@@ -76,6 +88,14 @@ _Avoid_: Confidence interval, error bar
 The share of wall-clock seconds inside monitoring periods whose usage-habit classification is known rather than unknown.
 _Avoid_: Uptime, sample count
 
+**Byte-allocation completeness**:
+Whether the available evidence establishes all monitored writes attributable to a specified span, without missing counter evidence or unknown boundary shares; distinct from usage-habit classification coverage.
+_Avoid_: Coverage, estimated allocation
+
+**Qualifying day**:
+A UTC date whose represented monitored time meets the coverage requirement for projection evidence. Qualification is provisional while the date is in progress and does not establish byte-allocation completeness.
+_Avoid_: Completed day, supported day, calibration day
+
 **Collection run**:
 One scheduled or on-demand execution of the collector that interrogates the drive and extends the observation history.
 _Avoid_: Poll, daemon tick