Antispam C1: the API and the three UI surfaces

Completes phase C1 — until now the plugin classified mail that nobody could see
or steer.

Router (§C.6): settings with merge semantics, allow/deny rules, a per-message
verdict lookup, learn, and stats. Two behaviours worth naming. A banner
threshold above the move threshold is silently capped rather than refused,
because a banner past the move score can never be seen — everything that far up
is already in Junk. And /learn moves the message even when the engine is
unreachable: teaching is best-effort, but filing is what the user actually
asked for.

UI: settings.page (thresholds in plain language, per-account toggles, the two
lists, the privacy switch, activity); message.banner for the uncertain middle,
offering Move to Junk / Not spam / Always trust sender; message.actions with
Spam / Not spam. The banner mounts on every message but renders only for a
`banner` verdict — a spam warning on ordinary mail is worse than no warning.

Bundle serving is allow-listed by filename, so /ui/../hook.py is a 404 rather
than a file read.

Tests cover the defaults, merge semantics, the threshold cap, rule
normalisation and idempotency, stats degrading to empty when Rspamd is absent,
and RLS isolation: one user cannot see another's rules or settings, nor delete a
rule whose id they know.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018SqJYt7jD7oUEkoY68sBZo

plugins/webmail_plugin_antispam/webmail_plugin_antispam/schemas.py

@@ -0,0 +1,60 @@
+"""Request/response models for the antispam API (SPEC §C.6)."""
+
+from __future__ import annotations
+
+import uuid
+
+from pydantic import BaseModel, Field
+
+
+class SettingsOut(BaseModel):
+    enabled_accounts: list[str]
+    move_threshold: float
+    banner_threshold: float
+    network_checks: bool
+    learn_from_provider_junk: bool
+
+
+class SettingsIn(BaseModel):
+    """Merge semantics: omitted fields keep their current value."""
+
+    enabled_accounts: list[str] | None = None
+    # Bounds are guard rails, not opinions: 0 would file everything as spam and
+    # the engine's own scale tops out well below 100.
+    move_threshold: float | None = Field(default=None, gt=0, le=100)
+    banner_threshold: float | None = Field(default=None, gt=0, le=100)
+    network_checks: bool | None = None
+    learn_from_provider_junk: bool | None = None
+
+
+class RuleOut(BaseModel):
+    id: uuid.UUID
+    kind: str
+    pattern: str
+
+
+class RuleIn(BaseModel):
+    kind: str = Field(pattern="^(allow|deny)$")
+    # An address (a@b.test) or a whole domain (@b.test).
+    pattern: str = Field(min_length=3, max_length=320)
+
+
+class LearnIn(BaseModel):
+    message_id: uuid.UUID
+    verdict: str = Field(pattern="^(spam|ham)$")
+
+
+class VerdictOut(BaseModel):
+    """What the banner slot needs to explain itself."""
+
+    message_id: uuid.UUID
+    score: float
+    action: str
+    symbols: list[str]
+    learned: str | None
+
+
+class StatsOut(BaseModel):
+    counts: dict[str, int]
+    top_symbols: list[dict[str, object]]
+    bayes: dict[str, object] | None