Insert a working repeat block instead of its description

The placeholder chooser showed repeat blocks as "{{#claims}} … {{/claims}}" and
inserted exactly that on double-click -- the ellipsis is a label, so the saved
template rendered a literal "…" per claim instead of the claim.

Chooser rows are data now: each carries the text it reads as and, separately,
the snippet it inserts. A block contributes a complete, ready-to-edit block with
a sample line built from its own placeholders, and lands on a line of its own
when the cursor sits behind existing text.

Covered from both sides: the snippets are checked against the template validator
and renderer, and a UI test drives the real dialog -- insert, save, send -- and
asserts the mail carries actual claim lines. The Tk tests share one root (the
icon library binds its images to the first one) and skip without a display.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/ccma/domain/mail_templates.py

@@ -26,6 +26,33 @@ class MailTemplate:
     body: str
 
 
+@dataclass(frozen=True, slots=True)
+class MailTemplateBlock:
+    name: str
+    description: str
+    # Placeholder name -> short explanation, valid inside this block only.
+    placeholders: tuple[tuple[str, str], ...]
+    # The line the inserted block starts out with. It makes the inserted snippet a
+    # working block that renders real content -- the board edits this line rather
+    # than having to write the whole construct by hand.
+    sample: str
+
+    @property
+    def snippet(self) -> str:
+        return f"{{{{#{self.name}}}}}\n{self.sample}\n{{{{/{self.name}}}}}\n"
+
+
+@dataclass(frozen=True, slots=True)
+class PlaceholderEntry:
+    """One row of the options dialog's placeholder chooser: what it reads as, and
+    what double-clicking it puts into the template."""
+
+    label: str
+    snippet: str
+    description: str
+    indented: bool = False
+
+
 @dataclass(frozen=True, slots=True)
 class MailTemplateSpec:
     key: str
@@ -36,8 +63,7 @@ class MailTemplateSpec:
     # dialog. The mail services must supply exactly these keys, so this doubles as
     # the contract a stored template is validated against.
     placeholders: tuple[tuple[str, str], ...]
-    # Repeat block name -> (explanation, item placeholders).
-    blocks: tuple[tuple[str, str, tuple[tuple[str, str], ...]], ...] = ()
+    blocks: tuple[MailTemplateBlock, ...] = ()
 
 
 BASE_PLACEHOLDERS: tuple[tuple[str, str], ...] = (
@@ -99,10 +125,11 @@ MAIL_TEMPLATES: tuple[MailTemplateSpec, ...] = (
             ("payment.reference", "Vorgeschlagener Verwendungszweck"),
         ),
         blocks=(
-            (
-                "claims",
-                "Wiederholt sich je ausgewählter Forderung",
-                CLAIM_ITEM_PLACEHOLDERS,
+            MailTemplateBlock(
+                name="claims",
+                description="Wiederholt sich je ausgewählter Forderung",
+                placeholders=CLAIM_ITEM_PLACEHOLDERS,
+                sample="{{claim.description}} (fällig {{claim.due_date}}): {{claim.balance}} Euro",
             ),
         ),
     ),
@@ -128,13 +155,14 @@ MAIL_TEMPLATES: tuple[MailTemplateSpec, ...] = (
             ("payment.reference", "Vorgeschlagener Verwendungszweck"),
         ),
         blocks=(
-            (
-                "reminder.items",
-                "Wiederholt sich je Mahnposition",
-                (
+            MailTemplateBlock(
+                name="reminder.items",
+                description="Wiederholt sich je Mahnposition",
+                placeholders=(
                     ("item.description", "Bezeichnung der Position"),
                     ("item.amount", "Betrag der Position"),
                 ),
+                sample="{{item.description}}: {{item.amount}} Euro",
             ),
         ),
     ),
@@ -157,6 +185,28 @@ MAIL_TEMPLATES: tuple[MailTemplateSpec, ...] = (
 )
 
 
+def placeholder_entries(key: str) -> list[PlaceholderEntry]:
+    """Rows for the placeholder chooser. Repeat blocks contribute a complete,
+    ready-to-edit block -- inserting one has to leave a working template behind,
+    not a description of one."""
+    spec = template_spec(key)
+    entries = [
+        PlaceholderEntry(f"{{{{{name}}}}}", f"{{{{{name}}}}}", description)
+        for name, description in spec.placeholders
+    ]
+    for block in spec.blocks:
+        entries.append(
+            PlaceholderEntry(
+                f"{{{{#{block.name}}}}} … {{{{/{block.name}}}}}", block.snippet, block.description
+            )
+        )
+        entries.extend(
+            PlaceholderEntry(f"{{{{{name}}}}}", f"{{{{{name}}}}}", description, indented=True)
+            for name, description in block.placeholders
+        )
+    return entries
+
+
 def template_spec(key: str) -> MailTemplateSpec:
     for spec in MAIL_TEMPLATES:
         if spec.key == key:
@@ -209,15 +259,12 @@ def validate_mail_template(key: str, subject: str, body: str) -> None:
     while editing the template instead of during a send run."""
     spec = template_spec(key)
     known = {name for name, _help in spec.placeholders}
-    block_names = {name for name, _help, _items in spec.blocks}
+    block_names = {block.name for block in spec.blocks}
     unknown: set[str] = set()
-    for block_name, _help, item_placeholders in spec.blocks:
-        for match in _blocks_of(body, block_name):
-            unknown.update(
-                name
-                for name in _placeholder_names(match)
-                if name not in known and name not in {item for item, _text in item_placeholders}
-            )
+    for block in spec.blocks:
+        block_known = known | {name for name, _help in block.placeholders}
+        for match in _blocks_of(body, block.name):
+            unknown.update(name for name in _placeholder_names(match) if name not in block_known)
     remaining = body
     for block_name in block_names:
         remaining = _strip_blocks(remaining, block_name)