Give the weekly difftest a fresh seed and a bigger budget

A fixed seed makes a weekly job re-check the same mutations forever, so it
defaults to the run id now. And the budget was set before the run was
measured: 3M checks take a minute and a half on four cores, so -per 60
-depth 3 is a few minutes for roughly 17M.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01JzBeCg7rjweVW3uGPg5G7T

Author: claude

.github/workflows/difftest.yml

@@ -14,11 +14,11 @@ on:
   workflow_dispatch:
     inputs:
       seed:
-        description: "PRNG seed"
-        default: "1"
+        description: "PRNG seed (default: the run id, so each run is new ground)"
+        default: ""
       per:
-        description: "mutations per corpus case"
-        default: "20"
+        description: "mutations per input"
+        default: "60"
 
 jobs:
   difftest:
@@ -33,8 +33,12 @@ jobs:
         with:
           path: .sqlite
           key: sqlite-${{ hashFiles('internal/sqlitesrc/sqlitesrc.go', 'internal/sqlitesrc/oracle/oracle.c') }}
+      # The seed defaults to the run id rather than to a constant: a weekly
+      # job with a fixed seed re-checks the same mutations forever. Roughly
+      # 17M checks, a few minutes on a four-core runner -- the oracle runs
+      # as a pool of batch-mode processes, so the cost is nearly all meyer.
       - run: >
           go run ./cmd/difftest
-          -per ${{ github.event.inputs.per || '20' }}
-          -depth 2
-          -seed ${{ github.event.inputs.seed || '1' }}
+          -per ${{ github.event.inputs.per || '60' }}
+          -depth 3
+          -seed ${{ github.event.inputs.seed || github.run_id }}