fix(server): backfill login shell for consistent agent env

[JoeyEamigh]

What Changed

backfill the login-shell environment at startup instead of just PATH

Why

depending on how the t3code environment was started, agents end up with different variables and functions in their shell. this can break things like nvm, fnm, custom shell functions, env vars you expect agents to have, etc. this shows up worst when i am using t3code over ssh to a main development box that i also use myself. i expect the agent to have access to shell and env that i set up for myself and work in claude code, codex, etc, but its missing in t3code.

claude's reasoning

What Changed

• apps/server now hydrates the whole login-shell environment at startup instead of PATH alone
• add readFullEnvironmentFromLoginShell to @t3tools/shared/shell, alongside the existing
  name-list reader, using the same -ilc probe with a NUL-delimited env -0 capture
• hydration is backfill-only: a variable the process already has is never overwritten
• PATH keeps its current mergePathEntries + launchctl behaviour, unchanged
• drop readPathFromLoginShell, which has no remaining callers

Why

On the same machine, as the same user, agents get a different environment depending on how the
server was started.

fixPath() recovers PATH and nothing else (apps/server/src/os-jank.ts). That is enough to
find an agent binary, which is what it was written for, but not enough to run one: anything the
user exports from their shell rc is evaluated by that login shell and then discarded.

It shows up worst on the remote path. packages/ssh/src/tunnel.ts launches the remote server with

nohup env T3CODE_NO_BROWSER=1 "$RUNNER_FILE" serve --host 127.0.0.1 --port "$REMOTE_PORT" ...

No login shell is involved, so the daemon holds only what sshd's non-interactive shell produced,
and every agent it spawns inherits that. On my machine the daemon has 110 variables where the
login shell has 161. Missing: EDITOR, NVM_DIR, NVM_BIN, GVM_ROOT, RBENV_SHELL, and the
rest of the version-manager state, because those are configured below the interactive guard in the
shell rc. 19c214645 describes that exact failure mode for the WSL backend and fixes it there.

The desktop side already solved its half of this: DesktopShellEnvironment captures 17 names.
The server never received the equivalent work — #972 says so directly, "the server-side startup
path is left unchanged so this PR stays desktop-scoped." This is that deferred half.

Why backfill rather than overwrite

An inherited value is the one the service was deliberately launched with, and for session-scoped
handles it is the correct one. #972 established this for SSH_AUTH_SOCK (a Terminal-launched
session must keep its own socket rather than take the login shell's), and the locale group in
DesktopShellEnvironment follows the same principle.

Backfill also means this composes with the desktop rather than fighting it. In a desktop install
the server inherits Electron's already-hydrated environment and only fills what is still missing,
so every precedence decision in DesktopShellEnvironment survives untouched.

Six names stay runtime-owned (HOME, PATH, PWD, OLDPWD, SHLVL, _) plus T3_*/T3CODE_*.
The login shell inherits this process's environment, so for those it reports its own values rather
than the user's configuration.

Scope

Server only, on purpose. DesktopShellEnvironment is untouched: it hydrates the Electron main
process for Electron's own needs, and agents are spawned by the server, so this reaches both
deployments without changing desktop behaviour.

Testing

• vp run --filter @t3tools/shared --filter t3 test — 5088 passed
• typecheck, lint, fmt --check, knip:check all clean
• new server tests mirror the desktop contract, including the SSH_AUTH_SOCK preservation case
  from DesktopShellEnvironment.test.ts

env -0 is used for the capture. It is supported by Apple's BSD env; verified on macOS 26.3,
and the app's floor is minimumSystemVersion: 13.0.

UI Changes

None.

Checklist

• This PR is small and focused
• I explained what changed and why

Summary by CodeRabbit

• Bug Fixes
  • POSIX environments now import a more complete set of variables from login shells.
  • Existing environment values are preserved, while missing or empty values can be populated automatically.
  • Runtime-managed variables remain protected from unintended changes.
  • Shell output is parsed more reliably, including values containing newlines, equals signs, and marker text.
  • Environment detection now handles shell lookup failures gracefully and retains the inherited environment.

[macroscopeapp]

Approvability

Verdict: Not approved

Macroscope's review found this PR not approvable — This changes the default POSIX server startup path so login-shell variables are imported and inherited by agent processes, rather than only repairing PATH. Because it broadly propagates arbitrary environment values and may include sensitive credentials, the runtime and data-flow impact merits human review.

^{You can add or adjust custom eligibility rules. Learn more.}

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📝 Walkthrough

Walkthrough

The change captures complete login-shell environments, parses validated NUL-delimited entries, and hydrates missing server environment variables. It excludes runtime-owned names and updates fixPath to use the new hydration flow.

Changes

POSIX environment hydration

Layer / File(s)	Summary
Full login-shell environment capture packages/shared/src/shell.ts, packages/shared/src/shell.test.ts	The shared shell utility captures env -0 output between markers, parses valid NAME=VALUE entries, applies a 5-second timeout and 4 MiB buffer, and replaces the PATH-only reader. Tests cover malformed entries, complex values, shell output, missing markers, and marker text inside values.
Server environment hydration apps/server/src/os-jank.ts, apps/server/src/os-jank.test.ts	hydratePosixEnvironment imports eligible missing values from the first usable login shell. It preserves inherited non-empty values, excludes runtime-owned and T3_/T3CODE_ names, and retains PATH fallback behavior. Tests cover success and failure cases.

Priority: ⬇️ Low

Estimated code review effort: 3 (Moderate) | ~25 minutes

Change: Bug fix

Sequence Diagram(s)

sequenceDiagram
  participant fixPath
  participant hydratePosixEnvironment
  participant LoginShell
  participant processEnvironment
  fixPath->>hydratePosixEnvironment: Hydrate POSIX environment
  hydratePosixEnvironment->>LoginShell: Read full login-shell environment
  LoginShell-->>hydratePosixEnvironment: Return parsed variables
  hydratePosixEnvironment->>processEnvironment: Fill eligible missing values

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Merge Risk: ⚪ Minimal · up to 46748

The server retains its existing startup fallback behavior when login-shell environment hydration cannot be used, and the reviewed hydration semantics match the covered tests. No actionable merge risk remains.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 9 functions across 4 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly summarizes the main change: backfilling the login-shell environment for consistent agent variables.
Description check	✅ Passed	The description includes the required What Changed, Why, UI Changes, and Checklist sections. It explains the implementation, scope, rationale, testing, and confirms that no UI changes are included.
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.

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Actionable comments posted: 1

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Inline comments:
In `@packages/shared/src/shell.ts`:
- Line 327: Update the end-marker search near FULL_ENV_CAPTURE_END to match the
NUL-delimited terminator (`\0` plus the marker and newline), preventing marker
text inside environment values from ending the capture early; add a regression
test covering an environment value containing the marker text.

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[JoeyEamigh]

one thing to note on the macroscope feedback here: while it is technically correct that it changes behavior, it actually brings it in line with npx t3. so any argument against this is also an argument against allowing npx t3 to continue inheriting the env vars of the parent shell.