compiler: lower polymorphic len() to wasm (string + array length)

[hyperpolymath]

Lower polymorphic len() to wasm (string + array length)

A string-wall residual found while verifying the migration corpus is actually unblocked: len() did not lower to wasm (Codegen.UnboundVariable "len") — only string_length did.

AffineScript arrays and strings share the same [len: i32][payload…] header (the list-concat handler already relies on this), so len() is the same single i32.load at offset 0 whether its argument is a String or an array. Merged into the existing string_length arm.

This unblocks the stdlib string layer on the wasm backend (starts_with/ends_with/substring/split/join/pad_* all call len() on strings; join also on arrays), which the corpus's String.length pattern (30 files) needs.

Verified: len("abcd")=4 and len([10,20,30])=3 lower and run; full run_codegen_wasm_tests.sh green (no regressions).

Separately noted (not fixed here): string ==/!= still lower to pointer comparison, not value comparison (string_sub(...) == "ab" is wrongly 0) — a #555-class interp-vs-wasm divergence, tracked for a follow-up slice. It only affects string-logic kernels; integer-brain extraction (strings kept host-side) is unaffected.

https://claude.ai/code/session_01WoKhFQePiRsAj7aqnxbG8s

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Generated by Claude Code

[github-actions]

🔍 Hypatia Security Scan

Findings: 40 issues detected

Severity	Count
🔴 Critical	2
🟠 High	22
🟡 Medium	16

⚠️ Action Required: Critical security issues found!

View findings

[
  {
    "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": "Issue in scorecard-enforcer.yml",
    "type": "scorecard_publish_with_run_step",
    "file": "scorecard-enforcer.yml",
    "action": "split_scorecard_publish_job",
    "rule_module": "workflow_audit",
    "severity": "high"
  },
  {
    "reason": "Issue in instant-sync.yml",
    "type": "secret_action_without_presence_gate",
    "file": "instant-sync.yml",
    "action": "peter-evans/repository-dispatch",
    "rule_module": "workflow_audit",
    "severity": "high"
  },
  {
    "reason": "Shell execution -- validate input before passing to shell (1 occurrences, CWE-78)",
    "type": "js_exec_sync",
    "file": "/home/runner/work/affinescript/affinescript/packages/affinescript-cli/mod.js",
    "action": "flag",
    "rule_module": "code_safety",
    "severity": "high"
  },
  {
    "reason": "Shell execution -- validate input before passing to shell (2 occurrences, CWE-78)",
    "type": "js_exec_sync",
    "file": "/home/runner/work/affinescript/affinescript/packages/affine-vscode/mod.js",
    "action": "flag",
    "rule_module": "code_safety",
    "severity": "high"
  },
  {
    "reason": "Shell execution -- validate input before passing to shell (1 occurrences, CWE-78)",
    "type": "js_exec_sync",
    "file": "/home/runner/work/affinescript/affinescript/affinescript-vite/src/affine-plugin-improved.js",
    "action": "flag",
    "rule_module": "code_safety",
    "severity": "high"
  },
  {
    "reason": "expect() in hot path (32 occurrences, CWE-754)",
    "type": "expect_in_hot_path",
    "file": "/home/runner/work/affinescript/affinescript/affinescriptiser/src/codegen/wasm_gen.rs",
    "action": "flag",
    "rule_module": "code_safety",
    "severity": "medium"
  },
  {
    "reason": "expect() in hot path (29 occurrences, CWE-754)",
    "type": "expect_in_hot_path",
    "file": "/home/runner/work/affinescript/affinescript/affinescriptiser/src/codegen/affine_gen.rs",
    "action": "flag",
    "rule_module": "code_safety",
    "severity": "medium"
  },
  {
    "reason": "unsafe block -- requires SAFETY comment (2 occurrences, CWE-676)",
    "type": "unsafe_block",
    "file": "/home/runner/work/affinescript/affinescript/runtime/src/panic.rs",
    "action": "flag",
    "rule_module": "code_safety",
    "severity": "medium"
  },
  {
    "reason": "unsafe block -- requires SAFETY comment (1 occurrences, CWE-676)",
    "type": "unsafe_block",
    "file": "/home/runner/work/affinescript/affinescript/runtime/src/alloc.rs",
    "action": "flag",
    "rule_module": "code_safety",
    "severity": "medium"
  }
]

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