* fix(slack): route DM thread replies to main session instead of thread-scoped session
DM thread replies (user replies inside a thread under a bot message in a
DM) were routed to a thread-specific session key instead of the user's
main DM session. This caused the agent to never receive the inbound on
the expected session, making the bot appear unresponsive.
The root cause was in prepare-routing.ts: canonicalThreadId for
isDirectMessage was set to threadTs when isThreadReply was true, creating
a session key like agent:main:slack:direct:u3🧵<ts>. DM threads
are a UI affordance — not a session boundary — so all DM messages should
route to the main DM session regardless of thread_ts.
Also adds a diagnostic logVerbose warning when assistant_app_thread
message_changed events fail sender resolution (Case 2 of #82390),
which was previously completely silent.
Fixes#82390
* chore(slack): polish DM thread routing PR
* test(slack): update DM thread routing contract
* test(slack): flatten non-main DM thread expectations
* fix(slack): preserve bound DM thread routes
* test(slack): align DM thread session fixtures
* fix(slack): keep flattened DM thread metadata scoped
* fix(slack): preserve DM thread delivery routes
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Co-authored-by: Peter Steinberger <steipete@gmail.com>
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