fix(tirith): skip auto-install on Termux native (Bionic libc)

[briandevans]

Summary

• Detect Termux native (PREFIX=/data/data/com.termux/files/...) in _detect_target() and short-circuit to None so the linux-gnu binaries — whose dynamic interpreter /lib/ld-linux-*.so.* doesn't exist on Termux's Bionic-libc filesystem — are never downloaded.
• Surface a distinct termux_native_unsupported reason from _install_tirith() plus an actionable INFO log pointing the user at proot Ubuntu or TIRITH_ENABLED=false.
• 7 focused regression tests covering true/false detection, the Termux/Android system-string variants, the proot-Ubuntu pass-through, and the install-side reason tag.

Fixes #26275.

The bug

Issue #26275: hermes-agent on Termux for Android 26 (aarch64) emits

WARNING tools.tirith_security: tirith spawn failed: [Errno 2] No such file or directory: '/data/data/com.termux/files/home/.hermes/profiles/vira/bin/tirith'

— even though the binary file is present at the path. The reporter pinned this down via file tirith:

tirith: ELF 64-bit LSB pie executable, ARM aarch64, ... interpreter /lib/ld-linux-aarch64.so.1, ...

The kernel can't load /lib/ld-linux-aarch64.so.1 (Termux has no /lib at all — its filesystem lives entirely under /data/data/com.termux/files/usr/), so it returns ENOENT for the interpreter, which Python surfaces as a FileNotFoundError whose path attribute is the binary's path, not the interpreter's. The error message is misleading; the binary is fine, the dynamic linker is missing.

The auto-installer downloaded that broken binary because commit 99af222ec (fix(tirith): detect Android/Termux as Linux ABI-compatible) opted Android into the unknown-linux-gnu Rust target on the assumption that Bionic is ABI-compatible with glibc. It isn't, for any binary that's dynamically linked against glibc — the prebuilt tirith ELF embeds a glibc dynamic interpreter path that Termux can't satisfy.

The fix

Narrow the Linux/Android branch in _detect_target() to skip Termux native, detected via PREFIX=/data/data/com.termux/files/... (Termux's canonical env var, set by every Termux session). Inside a proot Ubuntu chroot on top of Termux, PREFIX is rewritten to the chroot's /usr and a real glibc is available, so that path is unaffected — verified by test_detect_target_proot_ubuntu_inside_termux_still_works.

_install_tirith() returns a distinct termux_native_unsupported reason so the disk failure marker is specific (rather than the generic unsupported_platform tag), and emits an INFO log telling the user the actual cause and three workarounds:

tirith auto-install: Termux native (Bionic libc) is unsupported;
the linux-gnu binary's dynamic interpreter (/lib/ld-linux-*.so.*) is not
present on Termux. Run inside a proot Ubuntu chroot, install tirith
manually, or set TIRITH_ENABLED=false.

A Conda-style PREFIX (e.g. /opt/conda/envs/dev) would NOT match — the prefix-string check is anchored at /data/data/com.termux/files/, verified by test_is_termux_native_false_for_unrelated_prefix.

Test plan

• Focused regression tests: tests/tools/test_tirith_security.py::TestTermuxNativeSkip — 7/7 pass
• Adjacent suite: tests/tools/test_tirith_security.py — 70/70 pass; tests/tools/test_command_guards.py tests/tools/test_yolo_mode.py — 38/38 pass
• Regression guard: with tools/tirith_security.py reverted via git stash, test_detect_target_returns_none_on_termux_native fails with AssertionError: assert 'aarch64-unknown-linux-gnu' is None, demonstrating the exact bug path from the issue. Restored fix → passes.

Related

• Fixes Bug: tirith spawn failed: [Errno 2] No such file or directory on Termux (Android) #26275
• Narrows commit 99af222ec (fix(tirith): detect Android/Termux as Linux ABI-compatible) which incorrectly assumed Bionic + glibc are ABI-compatible for dynamically-linked binaries.

[ygd58]

LGTM — dedicated _is_termux_native() helper and 7 regression tests make this the right approach. Closing my duplicate #26282 in favor of this PR.

[briandevans]

CI audit — all 3 Tests failures are pre-existing baselines on clean origin/main (db84a78). Zero failures are in touched code.

Test	Symptom	Root cause on main
tests/run_agent/test_provider_parity.py::TestDeveloperRoleSwap::test_developer_role_via_nous_portal	ValueError: Model has a context window of 15,000 tokens	Test instantiates Nous Portal with empty model=; fallback resolves to a 15,000-token context which trips the 64K minimum guard at run_agent.py:2349.
TestBuildApiKwargsNousPortal::test_includes_nous_product_tags	(same)	(same)
TestBuildApiKwargsNousPortal::test_uses_chat_completions_format	(same)	(same)

Reproduces locally on clean main; already being addressed by #26048. The e2e failure is similarly post-#25957 baseline, also covered by #26048.

[briandevans]

Housekeeping: closing to keep my open-PR set focused on actively-reviewed work. This has been open ~17d without maintainer review and the surrounding code has continued to move, so it's unlikely to land as-is. The underlying fix still stands — happy to reopen and rebase if it would be useful. Thanks!