sys: add bun.sys.termios wrapper for Android bionic

[robobun]

Problem

std.c.termios for .linux assumes the glibc/musl shape (cc[32] + trailing c_ispeed/c_ospeed, ~60B). bionic uses the raw kernel asm-generic/termbits.h struct:

#define NCCS 19
struct termios {
  tcflag_t c_iflag, c_oflag, c_cflag, c_lflag;
  cc_t c_line;
  cc_t c_cc[NCCS];
};  // 36B — no c_ispeed/c_ospeed; baud is in c_cflag CBAUD bits

The first 36 bytes are layout-compatible so tcgetattr/tcsetattr mostly work, but:

• writes to .ispeed/.ospeed land past bionic's struct and are silently ignored
• Terminal.zig reinitialises c_cflag (t.cflag = .{ .CREAD = true, … }), zeroing the CBAUD bits → baud becomes B0

Fix

Same pattern as #30389:

• src/sys/sys.zig: add bun.sys.termios — on Android an extern struct matching bionic (cc: [19]u8, no speed fields, reusing std's tc_*flag_t since the bit layouts come from the kernel UAPI and are identical); elsewhere = std.posix.termios. Add bun.sys.tcgetattr/tcsetattr that @extern libc directly on Android and forward to std.posix.* elsewhere. A comptime tripwire fires if std.posix.termios ever loses .ispeed and shrinks to 36B, so the workaround can be dropped once the Zig stdlib gains a bionic case.
• src/runtime/api/bun/Terminal.zig: switch to bun.sys.termios/tcgetattr/tcsetattr; guard the .ispeed/.ospeed assignments with @hasField (it's a PTY, so baud is advisory only on bionic).
• src/md/ansi_renderer.zig: same swap for the kitty-graphics probe's termios save/restore.

Verification

• bun run zig:check-all — all 16 targets pass
• standalone zig build-obj -target {aarch64,x86_64}-linux-android -lc on the wrapper — bionic struct is 36B as expected, tripwire doesn't fire, flag-type reuse compiles
• bun bd test test/js/bun/terminal/ — all 121 tests pass
• new test/internal/termios-layout.test.ts opens a PTY master via posix_openpt, writes a sentinel into c_cc[VLNEXT] and toggles lflag.ECHO via bun.sys.tcsetattr, reads both back via bun.sys.tcgetattr. The round-trip holds iff Zig and libc agree on the struct layout.

No Android runtime test is included because the misbehaviour only surfaces on a real Android libc, which CI does not run; zig build check-android-debug (from #30389) compile-checks the struct once that lands.

[robobun]

^{Updated 3:40 AM PT - May 8th, 2026}

❌ @robobun, your commit 5f2af29 has 3 failures in Build #52786 (All Failures):

• test/js/bun/s3/s3-storage-class.test.ts - code 1 on 🍎 26 aarch64
• test/js/bun/s3/s3-storage-class.test.ts - code 1 on 🍎 14 aarch64
• test/js/bun/test/parallel/test-http-should-emit-close-when-connection-is-aborted.ts - timeout on 🪟 2019 x64
• test/js/bun/test/parallel/test-http-should-emit-close-when-connection-is-aborted.ts - timeout on 🪟 2019 x64-baseline
• test/js/bun/test/parallel/test-http-should-emit-close-when-connection-is-aborted.ts - timeout on 🪟 11 aarch64
• test/js/bun/shell/leak.test.ts - pid 5211 error: addresssanitizer on 🐧 13 x64-asan

---

🧪   To try this PR locally:

bunx bun-pr 30391

That installs a local version of the PR into your bun-30391 executable, so you can run:

bun-30391 --bun

[coderabbitai]

Walkthrough

Adds bun.sys-backed termios support (Android bionic layout fallback), migrates terminal code to bun.sys tcgetattr/tcsetattr, exposes a JSC testing hook and JS binding termiosLayout(), and adds a POSIX test that validates termios struct round-trip and field preservation.

Changes

Android-compatible termios support

Layer / File(s)	Summary
Core termios type and functions src/sys/sys.zig	Added pub const termios (Android: bionic-compatible extern struct; otherwise alias to posix.termios) and implemented pub fn tcgetattr / pub fn tcsetattr with Android @extern calls, INTR retry, and errno-to-error mapping; non-Android delegates to posix.
Terminal.zig PTY setup src/runtime/api/bun/Terminal.zig	Migrated createPtyPosix internals to use bun.sys.tcgetattr/bun.sys.tcsetattr; made baud-rate writes conditional on termios layout and updated internal getTermios/setTermios helpers.
ANSI renderer Kitty probe src/md/ansi_renderer.zig	Updated probeKittyGraphics() to save/restore stdin termios via bun.sys.tcgetattr and bun.sys.tcsetattr instead of std.posix equivalents.
JSC testing hook src/sys_jsc/error_jsc.zig	Added TestingAPIs.termiosLayout which opens a PTY, probes specific cc and lflag.ECHO entries, round-trips termios via bun.sys APIs, and returns { installed, readback, sizeof }.
JS test binding src/js/internal-for-testing.ts	Exposed TestingAPIs.termiosLayout as export const termiosLayout() returning undefined or { installed, readback, sizeof }.
Tests and documentation test/internal/termios-layout.test.ts	Added a POSIX-only test that calls termiosLayout(), asserts readback === installed, checks cc_lnext === 0x5a, and verifies sizeof > 0; includes explanatory comments about platform layout differences.

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately summarizes the main change: adding a bun.sys.termios wrapper specifically for Android bionic compatibility.
Description check	✅ Passed	The description fully addresses both template sections with clear problem statement, detailed fix explanation, and comprehensive verification steps including compile checks and test results.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

---

_{Comment @coderabbitai help to get the list of available commands and usage tips.}

[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@test/internal/termios-layout.test.ts`:
- Line 33: Replace the full-struct equality check between result!.readback and
result!.installed with targeted assertions that only verify intended invariants:
assert that readback.cc_lnext equals installed.cc_lnext and that the ECHO flag
bit in readback.c_lflag matches installed.c_lflag (use the ECHO
constant/bitmask), and remove the expect(result!.readback).toEqual(...) line;
this ensures the test verifies the round-trip of the specific control character
and preservation of the ECHO bit without relying on cross-libc-normalized
fields.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: ASSERTIVE

Plan: Pro

Run ID: c455073e-aa0a-4d68-8b06-b5d957ca24d5

📥 Commits

Reviewing files that changed from the base of the PR and between 1c6f79a and 5f2af29.

📒 Files selected for processing (1)

• test/internal/termios-layout.test.ts