fix(cli): match Go's init error texts for already-exists and orioledb gate (CLI-1986)

[Coly010]

What changed

supabase init's two error paths on the legacy shell now byte-match the Go CLI (verified by building and running apps/cli-go locally):

1. Config already exists (no --force) — was a friendlier TS-only message; now:

   failed to create config file: open supabase/config.toml: file exists
   Run supabase init --force to overwrite existing config file.
   

   This is Go's wrapped O_EXCL *os.PathError from utils.InitConfig (config.go:243-246) plus the CmdSuggestion from internal/init/init.go:38-42. The path is Go's relative utils.ConfigPath, so it's constant regardless of cwd/--workdir.

2. --use-orioledb without --experimental — was The --use-orioledb flag requires --experimental.; now cobra's message from Go's PreRun MarkFlagRequired("experimental") (cmd/init.go:32-36):

   required flag(s) "experimental" not set
   Try rerunning the command with --debug to troubleshoot the error.
   

   The second line is Go's generic recoverAndExit debug hint, which the legacy text output layer already appends when an error carries no suggestion. This follows the same handler-level convention as db dump's data-only gate and vanity-subdomains' desired-subdomain gate (bare message, no Error: prefix — matching Go's SilenceErrors + recoverAndExit rendering, verified against the built binary).

Also fixed while there (issue scope): the shared gitignore append now always prepends \n when supabase/.gitignore exists — even when it's empty — matching internal/init/init.go:80-96 (verified against the built Go binary).

Shell-scoping decision

The shared initProject module stays mechanism-only (it already returned { created: false } and left error shaping to each shell). Error shaping lives at each shell's handler boundary:

• Legacy gets new legacy-scoped error classes in legacy/commands/init/init.errors.ts with Go's exact bytes.
• Next deliberately keeps its friendlier texts: the graceful Supabase project already initialized. no-op and The --use-orioledb flag requires --experimental. — now pinned by tests. Its InitExperimentalRequiredError moved from shared/ to next/commands/init/init.errors.ts since it's next-only after this change; the now-unused shared InitAlreadyExistsError was deleted.

The gitignore newline fix is in shared code and applies to both shells (mechanical scaffolding, same bytes as Go).

Notes / deliberately left open

• Windows: byte parity for the already-exists message now covers Windows too (as of 6d26256) — init.handler.ts selects the message on RuntimeInfo.platform, rendering Go's filepath.Join-built path and ERROR_FILE_EXISTS errno text (failed to create config file: open supabase\config.toml: The file exists.), pinned by an integration test with a mocked win32 platform. Documented in SIDE_EFFECTS.md.
• Pre-existing, out of scope (flagged during review): normalize-error.ts's MissingOption case renders Error: required flag(s) … not set with an Error: prefix, while the built Go binary prints no prefix via recoverAndExit — worth a separate parity check; apps/cli/CLAUDE.md's porting checklist quotes a stale debug-hint wording ("get more details" vs the actual "troubleshoot the error"); Go's failed to read git ignore file error branch for an unreadable existing .gitignore remains unported.

Fixes CLI-1986
Linear: https://linear.app/supabase/issue/CLI-1986/init-error-texts-diverge-from-go-already-exists-use-orioledb-gate

[Coly010]

@codex review

[chatgpt-codex-connector]

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Reviewed commit: 2b81bf4ce3

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[Coly010]

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. Already looking forward to the next diff.

Reviewed commit: 6d26256946

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[github-actions]

Supabase CLI preview

npx --yes https://pkg.pr.new/supabase/cli/supabase@08a5c9ace8a14f0797fc71f78443522a9d06f59d

Preview package for commit 08a5c9a.

[kanadgupta]

Claude verified it all works as expected so LGTM. It did flag one small issue (see below):

One real issue (inline): SIDE_EFFECTS.md still says the Windows form is not reproduced, which the follow-up commit 6d26256 made stale; the PR description's Windows note is similarly outdated.