fix(driver): reject unavailable page source

[BenSheridanEdwards]

Fixes #149

Summary

• Preserves browser.getPageSource() failures instead of converting them to empty XML.
• Prevents unavailable page source from falsely satisfying negative locator assertions.
• Adds iOS and Android regression coverage for persistent failure, polling recovery, positive/negative assertions, and legitimate absence.

Proof

• npm run check — Biome checked 57 files; TypeScript passed.
• npm test — 230 passed, 0 failed.
• Generated project/device proof, or N/A: N/A — this changes non-rendered WebdriverIO error propagation. Device lanes were deliberately not used; observable matcher tests and a fresh packed-package consumer cover both platform branches without claiming device proof.

Better than exact main

Exact baseline: dfa57e72047c155a97e512121ed8608368108597.

With the new regression tests applied to that baseline:

✖ wdioDriver ios source failures cannot satisfy positive or negative assertions
✖ wdioDriver ios assertions recover before deciding presence or absence
✖ wdioDriver android source failures cannot satisfy positive or negative assertions
✖ wdioDriver android assertions recover before deciding presence or absence
ℹ tests 18
ℹ pass 14
ℹ fail 4

On this PR head:

✔ wdioDriver ios source failures cannot satisfy positive or negative assertions
✔ wdioDriver ios assertions recover before deciding presence or absence
✔ wdioDriver ios distinguishes legitimate absence from source unavailability
✔ wdioDriver android source failures cannot satisfy positive or negative assertions
✔ wdioDriver android assertions recover before deciding presence or absence
✔ wdioDriver android distinguishes legitimate absence from source unavailability
ℹ tests 18
ℹ pass 18
ℹ fail 0

Observable change: persistent source failure now rejects positive and negative assertions with the original source error; a transient failure is retried; a negative assertion passes only after a successful snapshot proves absence. A fresh consumer installed from npm pack recovered on the second source read and then proved legitimate absence for both iOS and Android.

Reviewer view

• Smallest source-verified view for a non-trivial PR, or Not applicable with the reason for a trivial PR: review wdioDriver.source and the six platform-parameterized assertion cases; no locator, expect, config, or CLI implementation changed.
• Source files, symbols, states, or commands that verify the view: src/driver.ts (Driver.source, wdioDriver); test/driver.test.ts; node --import tsx --test test/driver.test.ts; npm run check; npm test; npm run build.

Risk

• Risk is limited to callers that depended on a failed WebdriverIO source read looking like an empty hierarchy; those calls now reject, which is the safety contract.
• Existing waitUntil recovery remains unchanged and retries transient source errors. Successful empty/absent snapshots still satisfy negative assertions.
• GitNexus detect-changes: 2 files, 3 symbols, 3 affected flows; medium risk (Locator → WdioDriver, Launch → WdioDriver, Navigate → WdioDriver).
• Rollback: revert commit eef00117adac9c705e9ef8084e4e62b818709159.

Notes

• Full device coverage not run: explicitly omitted to avoid competing for device lanes; no device result is claimed.
• Duplicate sweep found no competing assertion-safety issue or PR. fix(locator): honor native visibility #126 concerns hidden/offscreen source attributes and tap visibility, not source-command failure.
• Independent model review was attempted but unavailable in this environment (Claude CLI unauthenticated; delegated reviewer scope denied). The focused regression, full repository gates, baseline sabotage proof, and packed-consumer proof were run locally.

PR Proof Law

• I followed .agents/DEFINITION_OF_DONE.md and .agents/skills/pr-inline-screenshot-proof/SKILL.md.
• Screenshots are committed and embedded inline with ![alt](...png?raw=1), or the proof section says Not applicable with the technical reason.
• The PR body has no bare screenshot links, local paths, relative paths, or proof placeholders.