feat: FC links a conclusive pair itself instead of asking (4392)

Operator, 2026-09-24: *"I don't want this to be manual that defeats the
convenience that I'm going for."*

Confirm-only was right while every signal was circumstantial. Time proximity
and a body that mentions Discord can never be more than suggestive, so asking
was the honest response to what FC actually knew. A shared working name is
different in kind: when the creator's own name for a piece appears in exactly
these two posts and nowhere else in their library, there is nothing left for
the operator to adjudicate, and asking is a chore FC invented for them.

AUTO_LINK_FLOOR is 1.0 and sits deliberately above IDENTITY_FLOOR's 0.75. The
gap between them IS the review queue — real evidence, not certain enough for
FC to act on alone. Measured on artist 8, of 15 name-sharing pairs: 11 are
conclusive, 2 more propose, 2 fall short of both.

Three refusals, because an auto-link is FC asserting something the operator
never saw:

  * Exactly one candidate may be conclusive. Two is not a tie to be broken by
    score — one post can tease two pieces dropped separately, and then each
    drop carries a different name from the same teaser, each individually
    conclusive. Two conclusive answers to "which drop is this" means the
    question was wrong, so both queue and FC says nothing.
  * Neither end may already be claimed by an accepted link. That link is the
    operator's decision and reassigning its other end would overrule them
    silently.
  * The whole thing is one setting, defaulting on, reversible in the UI —
    an accepted link is a row they can dismiss.

`match_post` now returns (proposed, linked) so a sweep can report what it did
on its own rather than only what it queued.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LVjrnpQjRgHdvq95rASoiR

backend/app/tasks/maintenance.py

@@ -1184,12 +1184,16 @@ def group_discord_drops() -> str:
     soft_time_limit=900, time_limit=1200,
 )
 def match_post_associations() -> str:
-    """Milestone 388 E5: propose which Patreon post announced which Discord drop.
+    """Milestone 388 E5: which Patreon post announced which Discord drop.
 
-    Proposes only — every pair lands in a review queue and nothing is linked
-    until the operator accepts. Maintenance lane for the same reason as the
-    grouper: no inference, no ML library, and it must not depend on the
-    optional ml-worker being present.
+    A CONCLUSIVE pair — one the creator's own working name identifies, where
+    that name appears in these two posts and nowhere else in their library — is
+    linked outright when `discord_link_auto` is on, because there is nothing
+    there for the operator to adjudicate. Everything weaker lands in the review
+    queue and stays unlinked until they accept it.
+
+    Maintenance lane for the same reason as the grouper: no inference, no ML
+    library, and it must not depend on the optional ml-worker being present.
     """
     import asyncio