fix(cli): warn when PowerShell mangles piped dumps

[7ttp]

TL;DR

Windows PowerShell 5.1 re-encodes piped native stdout and corrupts multi-byte UTF-8 in db dump output
so: added one stderr warning pointing at --file, only when a piped Windows dump actually contains non-ASCII bytes...

ref

• closes CLI-2277 CLI-2276
• closes DB Dump Corrupting Unicode Characters #6397

[chatgpt-codex-connector]

💡 Codex Review

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[github-actions]

Supabase CLI preview

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[7ttp]

/ai-review

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Superseded by a newer AI review

🤖 AI Review

Seven reported findings deduplicate to six. All are confirmed: the main concern is that the Windows shell heuristic is both over- and under-inclusive; the remaining items are a production-layer test gap and four nits. No critical or major issue was found.

Findings

Severity	Location	Category	Sources	Claim
🟡 MINOR	apps/cli/src/legacy/commands/db/dump/dump.handler.ts:276	correctness	claude+codex	The pipe heuristic cannot identify the redirecting shell: it warns for byte-faithful Windows pipes and suppresses warnings when MSYS/mintty variables are inherited by a PowerShell child.
🟡 MINOR	apps/cli/src/shared/runtime/tty.layer.ts:11	test-coverage	claude	The production stdout pipe-detection primitive is untested, while command tests replace it with a mocked stdoutIsPipe value.
⚪ NIT	apps/cli/src/legacy/commands/db/dump/dump.handler.ts:279	correctness	claude	An explicitly empty MSYSTEM environment variable suppresses the warning as though an MSYS session had been detected.
⚪ NIT	apps/cli/src/legacy/commands/db/dump/dump.handler.ts:338	readability	claude	The non-ASCII scan communicates its latched state indirectly by assigning on every iteration and relying on the loop condition to preserve a true result.
⚪ NIT	apps/cli/src/shared/runtime/tty.service.ts:6	documentation	claude	The stdoutIsPipe documentation is broader than its FIFO-only implementation and does not disclose that socket-backed stdout channels return false.
⚪ NIT	apps/cli/src/legacy/commands/db/dump/dump.handler.ts:276	code-quality	claude	The handler computes the pipe/env tracking gate for --file dumps even though that branch never scans stdout, and the tests do not explicitly pin silence for that combination.

Stats

Claude findings: 6 · Codex findings: 1 · Confirmed: 6 · Refuted: 0 · Uncertain: 0

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Models: claude-opus-5 + gpt-5.6-sol · Trigger: manual · Workflow run

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