feat(t-paliad-183): mig 084 — backfill condition_expr per design §2.4

Phase 3 Slice 2 Step B-3. Convert condition_flag text[] →
condition_expr jsonb per DESIGN §2.4 long form (NOT msg 1746's
short {"and":[...]} form — head clarified in msg 1750 that
design §2.4 wins because long form parses uniformly across
and/or/not, matching what the Slice-4 calculator + Slice-11 rule
editor will emit).

Mapping:
  ['with_ccr']                  →  {"flag":"with_ccr"}              (5 rows)
  ['with_amend']                →  {"flag":"with_amend"}            (4 rows)
  ['with_cci']                  →  {"flag":"with_cci"}              (4 rows)
  ['with_ccr', 'with_amend']    →  {"op":"and","args":[
                                       {"flag":"with_ccr"},
                                       {"flag":"with_amend"}
                                   ]}                                (4 rows)
  NULL or {}                    →  NULL                             (155 rows)

Total translated: 17 rows.

Single-flag is unwrapped (no AND wrapper) per design §2.4 — a
shortcut equivalent to a 1-arg AND that saves a layer of nesting
without losing semantics. The calculator's parser treats
{"flag":"<name>"} as the leaf and {"op":"<and|or|not>","args":[…]}
as the canonical boolean node.

jsonb construction uses jsonb_build_object + a LATERAL unnest…WITH
ORDINALITY over the flag array so args[] order matches the source
array exactly (load-bearing if a future migration adds order-
sensitive ops).

Idempotent via WHERE condition_expr IS NULL — re-running doesn't
double-write audit rows for already-translated rules. Migration
ends with a DO block that RAISE EXCEPTION if any non-empty
condition_flag row still has NULL condition_expr (catches a
broken translation path before it reaches Slice 4).

internal/db/migrations/084_backfill_condition_expr.down.sql

@@ -0,0 +1,14 @@
+-- t-paliad-183 down — reverts the condition_expr translations written
+-- by 084_backfill_condition_expr.up.sql. Mig 078 created the column
+-- with NULL on every row; resetting non-NULL values to NULL undoes the
+-- backfill cleanly (condition_flag is the source of truth for the
+-- legacy code path and stays untouched).
+
+SELECT set_config(
+    'paliad.audit_reason',
+    'rollback 084: reset condition_expr to mig 078 default (NULL)',
+    true);
+
+UPDATE paliad.deadline_rules
+   SET condition_expr = NULL
+ WHERE condition_expr IS NOT NULL;

internal/db/migrations/084_backfill_condition_expr.up.sql

@@ -0,0 +1,111 @@
+-- t-paliad-183 / Fristen Phase 3 Slice 2 Step B-3 — backfill
+-- paliad.deadline_rules.condition_expr from the legacy
+-- condition_flag text[] column per DESIGN §2.4 long form (NOT the
+-- short {"and":[...]} form sketched in head's msg 1746 — head's
+-- clarification msg 1750 rules in favour of the design doc).
+--
+-- Mapping (design §2.4):
+--
+--   condition_flag IS NULL OR array_length(_, 1) = 0
+--       → condition_expr stays NULL (unconditional, every rule renders)
+--
+--   array_length = 1, e.g. ['with_ccr']
+--       → condition_expr = jsonb '{"flag": "with_ccr"}'
+--         (single flag unwrapped — saves a layer of nesting that
+--          parses as the same boolean expression)
+--
+--   array_length >= 2, e.g. ['with_ccr', 'with_amend']
+--       → condition_expr = jsonb '{"op":"and","args":[
+--                                    {"flag":"with_ccr"},
+--                                    {"flag":"with_amend"}
+--                                ]}'
+--         (long form — same shape the rule editor will emit for OR /
+--          NOT in future rules so the calculator's parser is uniform)
+--
+-- Why long form on >=2: the calculator (Slice 4) reads
+-- {"op":"<and|or|not>","args":[...]} as the canonical boolean node and
+-- {"flag":"<name>"} as the leaf. Single-flag unwrap is a parse-time
+-- shortcut equivalent to a 1-arg AND. The short {"and":[...]} form in
+-- msg 1746 would require a per-key parser that doesn't generalise to
+-- OR / NOT. Design §2.4 long form is the load-bearing decision.
+--
+-- Live-data expected delta (172 rules total):
+--
+--   ['with_ccr']                 ×  5 rows → {"flag":"with_ccr"}
+--   ['with_amend']               ×  4 rows → {"flag":"with_amend"}
+--   ['with_cci']                 ×  4 rows → {"flag":"with_cci"}
+--   ['with_ccr', 'with_amend']   ×  4 rows → {"op":"and","args":[
+--                                              {"flag":"with_ccr"},
+--                                              {"flag":"with_amend"}
+--                                            ]}
+--   NULL or {}                   × 155 rows → stays NULL
+--
+--   Total touched: 17 rows.
+--
+-- Idempotent: WHERE condition_expr IS NULL guards re-runs against
+-- double-writing audit rows for already-translated rules.
+--
+-- jsonb construction: jsonb_build_object + jsonb_agg + a CASE on
+-- array_length keeps the long-form / unwrapped-flag split inline in
+-- one UPDATE. Per-flag jsonb leaf is built by a LATERAL unnest over
+-- the flag array so the args[] order matches the source array.
+
+SELECT set_config(
+    'paliad.audit_reason',
+    'backfill 084: condition_expr from condition_flag text[] per design §2.4 — '
+        || 'single flag unwrapped, multi flag long form {op:and, args:[...]}',
+    true);
+
+UPDATE paliad.deadline_rules dr
+   SET condition_expr = sub.expr
+  FROM (
+        SELECT dr_inner.id AS rule_id,
+               CASE
+                   -- Single flag: unwrapped leaf.
+                   WHEN array_length(dr_inner.condition_flag, 1) = 1
+                       THEN jsonb_build_object('flag', dr_inner.condition_flag[1])
+
+                   -- >=2 flags: long-form AND with args[] preserving order.
+                   WHEN array_length(dr_inner.condition_flag, 1) >= 2
+                       THEN jsonb_build_object(
+                           'op',   'and',
+                           'args', (
+                               SELECT jsonb_agg(jsonb_build_object('flag', f) ORDER BY ord)
+                                 FROM unnest(dr_inner.condition_flag) WITH ORDINALITY AS u(f, ord)
+                           )
+                       )
+
+                   -- Empty array (array_length=0) or NULL: leave NULL.
+                   ELSE NULL
+               END AS expr
+          FROM paliad.deadline_rules dr_inner
+         WHERE dr_inner.condition_flag IS NOT NULL
+           AND array_length(dr_inner.condition_flag, 1) > 0
+  ) AS sub
+ WHERE dr.id = sub.rule_id
+   AND dr.condition_expr IS NULL;
+
+DO $$
+DECLARE
+    n_total      int;
+    n_with_flag  int;
+    n_with_expr  int;
+    n_with_both  int;
+BEGIN
+    SELECT count(*),
+           count(*) FILTER (WHERE condition_flag IS NOT NULL AND array_length(condition_flag, 1) > 0),
+           count(*) FILTER (WHERE condition_expr IS NOT NULL),
+           count(*) FILTER (WHERE condition_flag IS NOT NULL AND array_length(condition_flag, 1) > 0
+                                AND condition_expr IS NOT NULL)
+      INTO n_total, n_with_flag, n_with_expr, n_with_both
+      FROM paliad.deadline_rules;
+    RAISE NOTICE 'backfill 084: total=%, with_condition_flag=%, with_condition_expr=%, both=%',
+                 n_total, n_with_flag, n_with_expr, n_with_both;
+    -- Hard assertion: every rule with a non-empty condition_flag now
+    -- has a non-NULL condition_expr (the inverse of the legacy column).
+    IF n_with_flag <> n_with_both THEN
+        RAISE EXCEPTION 'backfill 084: % rules carry condition_flag but no condition_expr — '
+                        'translation incomplete',
+                        n_with_flag - n_with_both;
+    END IF;
+END $$;