Precise Seam: new full-coverage policy for Seam Blocked (#16170)

* Precise Seam: new full-coverage policy for Seam Blocked

A Seam Blocked modifier that covers a whole perimeter now blocks it, like a
perimeter painted red all round, instead of being skipped. It overrides
painting and lower-priority modifiers, like Enforced and Neutral. A new
warning names the modifier: "Seam Blocked modifier "<name>" of "<object>"
covers an entire perimeter". It is shown only when a perimeter stays
entirely Blocked after all weak modifiers. The full-containment warning now
covers only Center, Left and Right.

* Precise Seam: fix seams on perimeters blocked all round

- SeamComparator::is_first_not_much_worse() compares the types first, so two
  Blocked candidates fall through like Neutral ones. On a perimeter blocked
  all round, by a whole Seam Blocked modifier or by red painting, Random put
  the seam on the closing vertex of every layer and Aligned stopped aligning.
- The whole-perimeter Blocked warning flags only the highest whole zone, the
  one in effect. A lower whole zone it overwrites is no longer reported, and
  the candidate scan runs only when that zone is Blocked.
- The warning msgids take the type name from the menu's "Seam Blocked" msgid.
- PreciseSeamWarnings::set() shares the load-before-store idiom, and every
  weak segment records its modifier.
- Tests: a whole Blocked perimeter gets the seams of an unmarked one under
  every seam position; overwritten whole Blocked zones are not reported.

---------

Co-authored-by: Ian Bassi <ian.bassi@outlook.com>

docs/HLSD/precise-seam.md

@@ -82,9 +82,7 @@ there.
   strong point is placed, no later strong modifier and no weak modifier is
   processed for that perimeter.
 - **Weak:** every weak modifier applies. They are applied from the lowest
-  priority to the highest, so the highest one overwrites overlapping zones. A
-  Blocked modifier that fully contains a perimeter is the exception: it is
-  skipped there (see [Full containment](#full-containment)).
+  priority to the highest, so the highest one overwrites overlapping zones.
 
 A strong modifier without a usable segment, even one whose fragments were all
 discarded, passes the turn to the next one.
@@ -232,20 +230,23 @@ begin and end positions on the source contour.
 ### Full containment
 
 A modifier that covers the whole perimeter has no boundaries on it. The policy
-follows seam painting, where painting a whole perimeter green is a meaningful
-choice and forbidding the seam all round is not:
+follows seam painting, where a whole perimeter can be painted in either color:
 
 - **Seam Enforced** types the whole perimeter, like a perimeter painted green all
   round, with subdivision applied as described under [Weak modifiers](#weak-modifiers).
 - **Seam Neutral** types the whole perimeter Neutral, like an unmarked perimeter,
   clearing painting and lower zones.
-- **Seam Blocked** is skipped for the perimeter, with the full-containment
-  warning. The seam cannot avoid the whole perimeter, so the modifier does not
-  override anything below it: lower zones and painting stay in effect.
-- **Seam Center, Left and Right** are skipped with the same warning: there is no
-  intersection to place the point on.
+- **Seam Blocked** types the whole perimeter Blocked, like a perimeter painted
+  red all round, overriding painting and lower zones. The seam cannot avoid such
+  a perimeter: the seam placer compares Blocked candidates with each other like
+  Neutral ones, so the seam is placed as on an unmarked perimeter. If the
+  perimeter stays Blocked after all weak zones, it is reported in the user
+  warning (see [Diagnostics and warnings](#diagnostics-and-warnings)), so the
+  user can check the modifier.
+- **Seam Center, Left and Right** are skipped with the full-containment warning:
+  there is no intersection to place the point on.
 
-Enforced and Neutral take part in the usual priority order (see
+Enforced, Neutral and Blocked take part in the usual priority order (see
 [Weak modifiers](#weak-modifiers)).
 
 The perimeter is fully contained when the united intervals cover every source
@@ -311,9 +312,9 @@ into every perimeter that has a strong seam.
 `collect_weak_modifier_segments()` extracts the segments of every weak modifier
 before the polygon is modified, so all positions refer to the same contour. Each
 segment becomes a zone with a type and two boundaries, kept in application
-order, lowest priority first. Full containment of an Enforced or Neutral
-modifier becomes a whole-perimeter zone at its place in that order: it has no
-boundaries and takes part in no insertion or helper step below. The boundaries
+order, lowest priority first. Full containment of a weak modifier becomes a
+whole-perimeter zone at its place in that order: it has no boundaries and takes
+part in no insertion or helper step below. The boundaries
 carry their positions on the source contour; these remain as provenance after
 insertion and are not indices into the modified polygon.
 
@@ -384,9 +385,10 @@ G-code export issues it as one non-critical warning with the ID
 `SlicingPreciseSeamWarning`. It is a single line, "Precise Seam: <causes>. Seam
 placement may differ from expected.", because the export warnings dialog shows
 only the first line of each warning. Repeated warning events replace the
-notification instead of appending to it. Except for the "had no effect" cause,
-the causes name the modifier types involved, as the menu names them, in menu
-order and each type once, for example "(Seam Left, Seam Enforced)".
+notification instead of appending to it. Except for the "covers an entire
+perimeter" and "had no effect" causes, the causes name the modifier types
+involved, as the menu names them, in menu order and each type once, for example
+"(Seam Left, Seam Enforced)".
 The causes are:
 
 - **failed to process some intersections (types):** at least one fragment was
@@ -395,8 +397,18 @@ The causes are:
   a Seam Center, Left or Right modifier had more than one segment on a
   perimeter (see [Strong modifiers](#strong-modifiers)).
 - **a perimeter is fully inside a modifier, the modifier was not applied to it
-  (types):** a Seam Center, Left, Right or Blocked modifier was skipped for a
+  (types):** a Seam Center, Left or Right modifier was skipped for a
   perimeter (see [Full containment](#full-containment)).
+- **Seam Blocked modifier "<name>" of "<object>" covers an entire perimeter:**
+  a Seam Blocked modifier covered a whole perimeter (see
+  [Full containment](#full-containment)). Only perimeters whose candidates are
+  all Blocked after all weak zones contribute to this warning, and only through
+  the zone in effect there: `apply_weak_modifiers_to_perimeter()` checks the
+  final types and flags the modifier of the highest whole-perimeter zone when it
+  is Blocked. A lower whole zone is overwritten by it and is not reported. Only
+  the first flagged modifier in print and volume order is named, followed by
+  "(N in total)" when there are several. The type name reuses the menu's
+  translation.
 - **modifier "<name>" of "<object>" had no effect on the seam (it might not reach
   the centerline of the printed perimeter):** a modifier was evaluated on at
   least one perimeter and never gave a segment, full containment or a discarded
@@ -420,6 +432,8 @@ The log records the following diagnostic markers:
 - `[PreciseSeamNoEffect]` for every modifier of the "had no effect" cause, with
   the object and modifier names. Unlike the user warning, the log lists all of
   them.
+- `[PreciseSeamFullyBlocked]` for every modifier of the "covers an entire
+  perimeter" cause, listed the same way.
 
 Failures and recoveries are counted separately. The first 10 of each per
 `init()` call are logged in detail, in parallel processing order; if a limit is
@@ -563,12 +577,14 @@ last modifier would.
   priorities, weak boundaries that coincide or share an edge, enforced
   subdivision, whole-perimeter weak zones with painting and priorities, weak
   zones over painting's oversampled candidates, the warning type masks, usage
-  tracking for the "had no effect" warning, volume sorting of strong and weak
-  groups, restoration of strong points after alignment, raft layer indexing and
-  structured slices. End-to-end tests slice a real object with Precise Seam
+  tracking for the "had no effect" and whole-perimeter Blocked warnings, volume
+  sorting of strong and weak groups, restoration of strong points after
+  alignment, raft layer indexing and structured slices. End-to-end tests slice
+  a real object with Precise Seam
   volumes and check the outer wall starts in the exported G-code: every strong
   mode under several seam positions and with a raft, Enforced and Blocked zones,
-  a modifier with a hole, and the user warning.
+  a perimeter blocked all round under every seam position, a modifier with a
+  hole, and the user warning.
 - [Seam placer tests](../../tests/fff_print/test_seam_placer.cpp) cover
   enforced-patch selection independent of the contour start, fully painted
   contours, duplicate removal, and `Print::apply()` synchronization through type