feat(parser): CORE-01 pt2 — &mut e exclusive-borrow surface (zero conflict delta)

[hyperpolymath]

CORE-01 pt2 — &mut e exclusive-borrow parser surface

Refs #177 (not Closes — the NLL/outer=&x analysis remains; it is
now expressible, no longer parser-gated).

Why

pt1 (#240) shipped shared-XOR-exclusive (UseWhileExclusivelyBorrowed,
ConflictingBorrow) but those rules could never fire from real
source: &mut e did not parse — only shared &e (OpRef) existed.
The pt2 residual was parser-gated. This adds the missing surface.

Change

File	What
ast.ml	new unary_op OpMutRef (&mut e) — borrow-checker-only distinction
parser.mly	expr_unary | AMP MUT e before AMP e — zero conflict delta (21 S/R + 1 R/R baseline held; AMP MUT unambiguous)
borrow.ml	OpMutRef ⇒ Exclusive borrow (the soundness payload); ref_target/is_copy match it
typecheck.ml / codegen.ml	OpMutRef folded into OpRef (typed TRef, same pointer codegen); gen_unop exhaustive

Verified

• &mut x parses ✓
• two &mut x → ConflictingBorrow ✓ (previously unrepresentable)
• read x while &mut x live → UseWhileExclusivelyBorrowed ✓
• return &mut local → BorrowOutlivesOwner ✓ (composes with pt2 return-escape)
• shared &x unchanged ✓; &mut x emits wasm (177 B) ✓
• Full gate 278 → 281 (+3 hermetic tests + 3 fixtures); all stdlib
  AOT green — zero over-rejection

Scope (honest)

&-in-#{ literals and bare block-statements already parse on main.
The -> &T/&T type sigil is deliberately not added — ref T/
mut T keyword types already express reference types; a &T sigil would
be duplicate surface (ADR territory, not a soundness gap). The pt2
residual is now the NLL / outer = &x dataflow analysis — now
expressible (surface unblocked), no longer parser-gated. Ledger +
in-code comment truthed.

🤖 Generated with Claude Code

[github-actions]

🔍 Hypatia Security Scan

Findings: 47 issues detected

Severity	Count
🔴 Critical	12
🟠 High	21
🟡 Medium	14

⚠️ Action Required: Critical security issues found!

View findings

[
  {
    "reason": "Stray AI.a2ml in root -- use 0-AI-MANIFEST.a2ml only",
    "type": "banned",
    "file": "AI.a2ml",
    "action": "delete",
    "rule_module": "root_hygiene",
    "severity": "high"
  },
  {
    "reason": "Superseded by 0-AI-MANIFEST.a2ml",
    "type": "banned",
    "file": "AI.djot",
    "action": "delete",
    "rule_module": "root_hygiene",
    "severity": "high"
  },
  {
    "reason": "Issue in quality.yml",
    "type": "missing_workflow",
    "file": "quality.yml",
    "action": "create",
    "rule_module": "workflow_audit",
    "severity": "high"
  },
  {
    "reason": "Issue in security-policy.yml",
    "type": "missing_workflow",
    "file": "security-policy.yml",
    "action": "create",
    "rule_module": "workflow_audit",
    "severity": "medium"
  },
  {
    "reason": "Action hyperpolymath/standards/.github/workflows/governance-reusable.yml@main needs attention",
    "type": "unpinned_action",
    "file": "governance.yml",
    "action": "pin_sha",
    "rule_module": "workflow_audit",
    "severity": "high"
  },
  {
    "reason": "Action actions/checkout@v4 needs attention",
    "type": "unpinned_action",
    "file": "publish-jsr.yml",
    "action": "pin_sha",
    "rule_module": "workflow_audit",
    "severity": "medium"
  },
  {
    "reason": "Action denoland/setup-deno@v2 needs attention",
    "type": "unpinned_action",
    "file": "publish-jsr.yml",
    "action": "pin_sha",
    "rule_module": "workflow_audit",
    "severity": "medium"
  },
  {
    "reason": "TypeScript file detected -- banned language",
    "type": "banned_language_file",
    "file": "/home/runner/work/affinescript/affinescript/affinescript-deno-test/example/smoke_driver.ts",
    "action": "flag",
    "rule_module": "cicd_rules",
    "severity": "critical"
  },
  {
    "reason": "TypeScript file detected -- banned language",
    "type": "banned_language_file",
    "file": "/home/runner/work/affinescript/affinescript/affinescript-deno-test/cli.ts",
    "action": "flag",
    "rule_module": "cicd_rules",
    "severity": "critical"
  },
  {
    "reason": "TypeScript file detected -- banned language",
    "type": "banned_language_file",
    "file": "/home/runner/work/affinescript/affinescript/affinescript-deno-test/mod.ts",
    "action": "flag",
    "rule_module": "cicd_rules",
    "severity": "critical"
  }
]

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