fix: read /proc/self/environ so PSST_PASSWORD survives ptrace-based sandbox injection

[LucasRoesler]

Problem

psst unlock fails with "Failed to unlock vault" when PSST_PASSWORD is injected by a ptrace-based sandbox supervisor (e.g. nono in supervised mode), even though the variable is present in the process environment.

The root cause is a timing gap between Bun and ptrace injection. Bun snapshots process.env from envp[] very early in its startup sequence — before a ptrace supervisor has had a chance to write into the process environment. The injected variable is present in the kernel's live view (/proc/self/environ) but absent from process.env.

This affects any runtime that snapshots envp[] at startup (Bun, Go, JVM). It does not affect Node.js or bash, which call through glibc's getenv() and see the live environ pointer.

Reproduction

# 1. create a demo directory and init a vault
mkdir psst-demo && cd psst-demo
PSST_PASSWORD=demo-password-1234 psst init

# 2. add an example secret
echo "my-secret-value" | PSST_PASSWORD=demo-password-1234 psst set --stdin EXAMPLE_SECRET

# 3. verify it works normally outside the sandbox
PSST_PASSWORD=demo-password-1234 psst list
# ● EXAMPLE_SECRET
# 1 secret(s)

# 4. store the password where nono can inject it (1Password shown; secret-tool works too)
#    op item create --title psst-demo --vault Personal password=demo-password-1234

# 5. run inside the sandbox — nono injects PSST_PASSWORD via ptrace after execve()
nono run --env-credential-map 'op://Personal/psst-demo/password' PSST_PASSWORD --allow-cwd -- psst list

Before fix:

✗ Failed to unlock vault

After fix (with PSST_DEBUG=1):

[psst debug] native-env: /proc/self/environ has 86 entries, PSST_PASSWORD=present
[psst debug] unlock: PSST_PASSWORD=set(len=20)

Secrets

● EXAMPLE_SECRET

1 secret(s)

Changes

• Add src/vault/native-env.ts: reads /proc/self/environ at call-time and exposes getenvNative(name). Linux-only; returns null on other platforms. Result is cached after first read.
• In SqliteBackend.unlock(): fall back to getenvNative() when process.env.PSST_PASSWORD is unset, so injected credentials are found even if Bun missed them at startup.
• Fix unlock priority order: env var (both sources) → keychain. Previously keychain was checked first, which could fail or block inside a sandbox before the env var fallback was tried.
• Add PSST_DEBUG=1 logging to the unlock path (itself read via both sources) to make this class of failure diagnosable without rebuilding.