`_read_agnes_ca_pem()` decides whether the served fullchain.pem needs
trust-bootstrapping in the rendered setup prompt. Pre-fix it only
checked the leaf's *immediate* issuer against `certifi`'s trust store.
For Let's Encrypt that's the intermediate (R13), which `certifi` does
not ship — only roots are in trust stores. So a publicly-trusted LE
chain still tripped the "needs bootstrap" path and the setup prompt
emitted a step-0 TLS trust block + clone-fallback marketplace block
that no client actually needs (Bun-compiled `claude.exe`, system git,
Python via certifi all validate the chain through the bundled ISRG
Root X1).
Now we walk every cert in the fullchain (leaf + intermediates) and
return None the first time any cert's issuer is in the certifi trust
store — that captures the standard "leaf signed by intermediate signed
by publicly-trusted root" shape. Trusted subjects are read once into
a set for O(1) lookup. Self-signed (leaf.issuer == leaf.subject) and
private-CA chains (no chain link's issuer in certifi) keep their
previous "return PEM" behavior, so deployments that genuinely need
the bootstrap still get it.
Validated end-to-end against the live VM at
agnes-marustamyan.groupondev.com (LE R13 → ISRG Root X1):
- Let's Encrypt fullchain → has_ca=False (was True)
- Self-signed cert → has_ca=True
- Corporate-CA chain (private root) → has_ca=True
- Missing fullchain.pem → has_ca=False
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