docs(phase29ab): closeout P1-P9

docs/development/current/main/design/pattern6-7-contracts.md

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+# Pattern6/7 Contracts (SSOT)
+
+This document defines the **contract boundary** for Pattern6/7 extractors.
+It is the SSOT for `NotApplicable` vs `Freeze` decisions.
+
+## Common Rule
+
+- **NotApplicable**: shape mismatch (another pattern may apply)
+- **Freeze**: shape matches but contract is violated (fail-fast)
+
+Tags:
+- Pattern6: `[joinir/phase29ab/pattern6/contract]`
+- Pattern7: `[joinir/phase29ab/pattern7/contract]`
+
+## Pattern6 (ScanWithInit / MatchScan)
+
+Accepted shape:
+- `loop(i < s.length())` or `loop(i <= s.length() - needle.length())`
+- `if s.substring(i, i + 1) == needle { return i }`
+- step update exists and matches direction
+
+Freeze conditions:
+- step update missing
+- forward scan with step != `i = i + 1`
+- reverse scan with step != `i = i - 1`
+Note:
+- plan line is forward-only; reverse scans are currently treated as NotApplicable
+
+## Pattern7 (SplitScan)
+
+Accepted shape:
+- `loop(i <= s.length() - separator.length())`
+- `if s.substring(i, i + separator.length()) == separator`
+- then: `result.push(...)`, `start = i + separator.length()`, `i = start`
+- else: `i = i + 1`
+
+Freeze conditions:
+- then/else update contracts broken (start/i updates)
+- separator literal length != 1 (P0 scope)