fix(windows): strip quotes from repaired PATH

[rynfar]

On Windows a PATH repaired from the registry can contain quoted segments. Pylon
kept the quotes when splitting and rejoining, so the resulting entries did not
resolve and provider CLIs looked missing on machines whose PATH happened to be
quoted.

Quotes are now stripped from each segment as PATH is normalized, in both the
shared helper and the desktop shell environment.

Adopted from upstream pingdotgg/t3code#8746 (12fe2d6d0), cherry-picked clean.
packages/shared/src/shell.ts was identical to the upstream base; Pylon's
divergence in DesktopShellEnvironment.ts is in unrelated hunks.

Verified: vp test run --dir packages/shared packages/shared/src/shell.test.ts
(30 passed) and vp test run --dir apps/desktop apps/desktop/src/shell/DesktopShellEnvironment.test.ts
(15 passed).

Not verified on a Windows host — this machine is macOS. The change is exercised by
the unit tests above, which cover the quoted-segment cases.

Reviewed and integrated with Claude Opus 5 in Claude Code.

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[github-actions]

Thread transfer impact

✅ Thread transfer remains within every enforced ceiling.

Provider	Metric	Main baseline	This PR	Impact	PR ceiling
Codex	Total thread wire	13.6 KiB	13.5 KiB	−10 B (−0.1%)	15.1 KiB	✅
Codex	Thread snapshot wire	6.9 KiB	6.9 KiB	+7 B (+0.1%)	7.3 KiB	✅
Codex	Live turn WebSocket wire	6.6 KiB	6.6 KiB	−17 B (−0.3%)	7.8 KiB	✅
Codex	Live turn WebSocket decoded	57.2 KiB	57.2 KiB	0 B (0.0%)	66.4 KiB	✅
Codex	Live turn messages	10	10	0 (0.0%)	21	✅
Claude	Total thread wire	13.6 KiB	13.5 KiB	−45 B (−0.3%)	15.1 KiB	✅
Claude	Thread snapshot wire	6.9 KiB	6.9 KiB	−3 B (−0.0%)	7.3 KiB	✅
Claude	Live turn WebSocket wire	6.6 KiB	6.6 KiB	−42 B (−0.6%)	7.8 KiB	✅
Claude	Live turn WebSocket decoded	58.1 KiB	58.0 KiB	−44 B (−0.1%)	66.4 KiB	✅
Claude	Live turn messages	10	9	−1 (−10.0%)	21	✅

Baseline: 9ade80d · PR result: effbf20 · Source CI: success

Scenario and decoded snapshot size

10 historical turns, 5 command tools per turn, 878.9 KiB retained MCP result per historical turn, and a 1.05 MiB retained result in the measured turn.

• Codex decoded thread snapshot: 109.5 KiB
• Claude decoded thread snapshot: 110.2 KiB

Updated in place by a trusted workflow. PR artifacts are strictly validated and never executed.

[rynfar]

Adversarial review confirmed the core change is correct and that dedupe behaviour is unchanged (pathComparisonKey already stripped wrapping quotes), replaceAll is fine under target: ESNext, no caller depends on quotes surviving the merge, and both copies of the helper were kept in sync. Two edge-case findings, both fixed.

1. Quoted PATH entries containing the delimiter were destroyed. PATH=C:\bin;"C:\my;dir";C:\other previously survived the split/rejoin byte-for-byte, because the fragments kept their quotes. Stripping quotes after splitting on the raw delimiter turned it into four entries — dropping the real directory and injecting a relative dir resolved against the child process's cwd. The split now honours quoting, and an entry containing the delimiter is re-quoted on the way out, without which the joined value would just be re-split by consumers. Unbalanced quotes fall back to a plain split, since those are stray characters rather than quoting — that keeps the existing C:" case working instead of swallowing every later entry.

2. Degenerate fragments were emitted rather than dropped. C:" became C:, a drive-relative entry, so spawned providers searched the child's own directory — somewhere that previously never matched, since C:" was not a valid directory name. Bare drive letters are now dropped, and both the shared and desktop test expectations updated to match.

Re-verified: shell.test.ts 31 passed (including a new case for the quoted delimiter), DesktopShellEnvironment.test.ts 15 passed, @t3tools/shared and @t3tools/desktop typecheck clean.

Still not verified on a Windows host — this machine is macOS. The unit tests cover both cases.