test(config): cover Save/Load faults + clearAll (token-persistence integrity)

[LukasWodka]

The config-fault harness from the coverage audit — no production changes, root-proof fault injection (parent-is-a-file, path-is-a-directory, non-empty-dir) + one chmod case guarded by a non-root euid.

• Load (74%): corrupt JSON → parse error; an unreadable path (a directory) → read error.
• Save (~65%): un-creatable dir → error; read-only dir → temp-file creation error (the atomic-write fault — the most safety-relevant path); fully-empty profiles are pruned (and stay off disk on reload).
• clearAll (67%): removes existing; missing is a no-op; a non-empty dir at the path surfaces a remove error.

make ci green.

🤖 Generated with Claude Code

---

Note

Low Risk
Test-only coverage expansion for existing config behavior; no runtime or security logic changes.

Overview
Adds internal/config/fault_test.go only—no production code changes. Tests drive config I/O through TRACEBLOC_CONFIG_DIR and fault injection (corrupt JSON, path-as-directory, parent-is-a-file, read-only dir with a non-root skip, non-empty dir at the config path).

Load: corrupt JSON must return a parse error; when config.json is a directory, a read error—so the CLI never treats a broken file as “not signed in.”

Save: un-creatable config dir and read-only dir must fail (atomic write must not silently truncate tokens); fully empty profiles are pruned in memory and stay absent after reload.

clearAll: removes an existing file, no-ops when missing, and errors when the path is a non-empty directory.

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[LukasWodka]

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[saadqbal]

LGTM 👍 Good fault coverage on the token-persistence path — the atomic-write failure arms and the empty-profile prune round-trip are the ones that matter, and the error wording (parsing/reading/creating) matches. Sensible root/euid skips.