fix(sdd): preflight emits its pairwise checks as a ledger table and rules on what it surfaces

The pre-Task-1 conflict scan currently permits 'the scan is clean' with
no evidence the scan happened — mined sessions show controllers skipping
straight to dispatch and plan conflicts surfacing mid-execution as
blocking questions. Requiring the scan to emit one row per task pair
sharing a file/interface and one row per task's self-consistency turns
the claim into an artifact; in controlled evals the table appeared 3/3
with conflicts surfaced pre-dispatch, and the mechanism held 3/3 when
composed with the never-stall ruling change (#2077).

Claude-Session: https://claude.ai/code/session_0185AJr98gHx5EmwqNeft4Sy

skills/subagent-driven-development/SKILL.md

@@ -142,17 +142,24 @@ a ledger file, not only in todos.
 Read the plan once, note its context and Global Constraints, and create a
 todo per task.
 
-Before dispatching Task 1, scan the plan once for conflicts:
+Before dispatching Task 1, scan the plan once for conflicts, writing down
+what you checked as you check it:
 
 - tasks that contradict each other or the plan's Global Constraints
 - anything the plan explicitly mandates that the review rubric treats as a
   defect (a test that asserts nothing, verbatim duplication of a logic block)
 
-Present everything you find to your human partner as one batched question —
-each finding beside the plan text that mandates it, asking which governs —
-before execution begins, not one interrupt per discovery mid-plan. If the
-scan is clean, proceed without comment. The review loop remains the net for
-conflicts that only emerge from implementation.
+The scan's output is a table, not a verdict. One row for every pair of tasks
+that share a file or an interface: the two tasks, what one produces against
+what the other consumes, and what you found. One row for every task: whether
+its own text agrees with itself — the tests it specifies against the code it
+specifies, the files it creates against the files it later touches. "The scan
+is clean" without those rows is not a scan you ran.
+
+Write the table to the ledger. Rule on each conflict it surfaces — the spec
+is the binding authority, the plan is its argument — record the ruling beside
+its row, and dispatch Task 1. The review loop remains the net for conflicts
+that only emerge from implementation.
 
 ## Model Selection