FN-7688: add slow login-shell profile latency hint and docs
Investigated whether --login in TerminalService first-prompt latency is a meaningful contributor and added a one-time diagnostic hint plus documentation of findings. - Add SLOW_LOGIN_PROFILE_HINT_MS (2000ms) threshold and one-time, non-blocking console.info hint in createSession()'s PTY onData handler when a login shell is slow to produce first output - Track spawnStartedAt and loginProfileHintLogged per session, and whether the succeeding spawn attempt used --login, without altering spawn args, timeouts, or the retry-without-login fallback - Add regression tests covering the slow-login-profile hint behavior in terminal-service.test.ts - Document the investigation and findings in docs/solutions/developer-experience/login-shell-profile-latency.md and link it from docs/dashboard-guide.md - Add a patch changeset for @runfusion/fusion describing the new server-log hint Files changed: .changeset/fn-7688-login-shell-profile-latency.md | 7 ++ docs/dashboard-guide.md | 17 +++ .../login-shell-profile-latency.md | 79 ++++++++++++++ .../src/__tests__/terminal-service.test.ts | 121 +++++++++++++++++++++ packages/dashboard/src/terminal-service.ts | 57 ++++++++++ 5 files changed, 281 insertions(+) Fusion-Task-Id: FN-7688 Fusion-Task-Lineage: 08d5dd47-ea9f-4973-9f0e-a8d5fdeae111 Co-authored-by: Fusion (runfusion.ai) <noreply@runfusion.ai>
This commit is contained in:
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.changeset/fn-7688-login-shell-profile-latency.md
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.changeset/fn-7688-login-shell-profile-latency.md
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@@ -0,0 +1,7 @@
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---
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"@runfusion/fusion": patch
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---
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summary: Add a one-time server log hint pointing to shell-profile-hygiene docs when a login shell is slow to prompt.
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category: performance
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dev: FN-7688 investigated whether `--login` in `TerminalService.detectShell()`/`createSession()` is a meaningful first-prompt latency contributor. Finding: negligible on lean profiles, additive (~800ms+) when `.zprofile`/`.bash_profile` eagerly sources something slow (e.g. version manager init). `--login` is preserved unconditionally per FN-7686; added `SLOW_LOGIN_PROFILE_HINT_MS` (2000ms) threshold and a one-time, non-blocking `console.info` hint in `createSession()`'s PTY `onData` handler — never alters spawn args, timeouts, or the `retry-without-login` fallback. See `docs/solutions/developer-experience/login-shell-profile-latency.md`.
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@@ -659,6 +659,23 @@ Features:
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### Slow first prompt / shell profile hygiene
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Fusion's embedded terminal spawns your shell as a **login shell** (`bash --login` / `zsh --login`) so `.bash_profile`/`.zprofile` (and, for interactive zsh, `.zlogin`) are sourced exactly as they would be in a real terminal. This is deliberate: dropping the login flag would silently break PATH entries, secrets, and tool init that many profiles rely on, so Fusion always tries `--login` first (falling back only if that specific spawn attempt fails, never as a latency optimization).
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If the terminal view appears almost instantly but stays blank for several seconds before the first prompt/output shows up, this is very rarely `--login` itself — measurements show the flag typically costs only single-digit milliseconds on a lean profile. The far more common cause is your own `.zprofile`/`.bash_profile` (or `.zshrc`/`.bashrc`, which a login shell also sources) eagerly running something slow, most often a version manager init script (`nvm.sh`, `rbenv init`, `pyenv init`, `direnv hook`, etc.). Because a **login** shell sources `.zprofile`/`.zlogin` in addition to `.zshrc` (a non-login shell skips them), anything slow specifically in `.zprofile`/`.bash_profile`/`.zlogin` is fully additive latency that only a login shell pays.
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To trim a slow first prompt:
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1. Move slow, one-time setup (build tool version managers, background daemons, etc.) out of `.zprofile`/`.bash_profile` and into `.zshrc`/`.bashrc`, or gate it behind an interactive-only check if it should not run for every login shell.
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2. Prefer lazy-loading over eager-sourcing for version managers — most (nvm, pyenv, rbenv) document a lazy-init pattern that defers the expensive part until the tool is first invoked.
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3. Time your own profile to confirm the source of the delay: `time zsh -i -c exit` (interactive, non-login) vs. `time zsh -li -c exit` (interactive, login) isolates whether `.zprofile`/`.zlogin` specifically is the slow part.
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4. If Fusion's server log shows a one-time `login shell took <N>ms to produce first output` hint for a session, it is pointing at this same profile-hygiene question — it is informational only and never blocks or retries the session.
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See `docs/solutions/developer-experience/login-shell-profile-latency.md` for the underlying measurement and the decision to keep `--login` unconditionally.
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## Git Manager
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## Git Manager
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Git Manager centralizes repo operations in the dashboard. On desktop/tablet it is available as an embedded right-dock panel and can expand into a resizable modal; on mobile it opens from the compact More surfaces.
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@@ -0,0 +1,79 @@
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---
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title: "Login-shell --login first-prompt latency: measurement and decision"
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date: 2026-07-08
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category: developer-experience
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module: packages/dashboard/src/terminal-service.ts
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problem_type: performance_investigation
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component: embedded_terminal
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applies_when: "Investigating why the embedded terminal's first prompt/output is slow to appear, specifically whether the `--login` shell flag in detectShell()/createSession() is the cause."
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symptoms:
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- "Terminal view renders immediately but shows no output for multiple seconds"
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- "Suspicion that bash/zsh --login profile sourcing is the bottleneck"
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root_cause: user_profile_content_not_the_login_flag
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resolution_type: documented_finding_plus_additive_diagnostic
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severity: low
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related_components:
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- packages/dashboard/src/terminal-service.ts
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- packages/dashboard/src/__tests__/terminal-service.test.ts
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tags: [terminal, login-shell, shell-profile, latency, pty, fn-7686, fn-7688]
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---
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# Login-shell `--login` first-prompt latency: measurement and decision
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## Problem
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FN-7686 (slow initial terminal load) flagged `detectShell()`'s use of `--login` for bash/zsh as a
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*possible but unconfirmed, environment-dependent* contributor to first-prompt latency, and deferred
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root-causing it. FN-7688 investigated this in isolation.
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## Investigation
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An ad hoc timed PTY harness (same `@homebridge/node-pty-prebuilt-multiarch` binding the dashboard
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bundles) measured wall-clock time from `pty.spawn()` to first readable output byte, for
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`bash`/`zsh` with and without `--login`, on (a) a typical/lean real developer profile and (b) a
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synthetic heavy profile (`ZDOTDIR` pointed at a temp dir whose `.zprofile`/`.zshrc` each `sleep 0.8`).
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Raw numbers and method are recorded in the FN-7688 task's `repro` document; summary:
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- **Typical/lean profile:** `--login` vs. non-login delta is single-digit milliseconds for both
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bash and zsh — noise-level, not perceptible.
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- **Heavy profile (simulated slow version-manager init):** `--login` costs an additional
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~815-820ms over non-login, because a login *interactive* zsh sources `.zshenv` → `.zprofile` →
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`.zshrc` → `.zlogin`, while a non-login interactive zsh sources only `.zshenv` → `.zshrc`. Any
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slow command placed in `.zprofile`/`.zlogin` (not `.zshrc`) is entirely additive cost that only
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exists because of `--login`.
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## Root cause
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`--login` itself is not a meaningful latency contributor on a typical/lean shell profile. It **is**
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a meaningful, user-environment-dependent contributor when the user's own `.zprofile`/`.bash_profile`
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eagerly sources something slow (most commonly a version manager init script: nvm/rbenv/pyenv/direnv).
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The mechanism is structural — a login shell sources strictly more profile files than a non-login
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shell — not a defect in `detectShell()`/`createSession()`.
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## Decision
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`--login` is preserved unconditionally (per FN-7686's hard constraint): dropping it would silently
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break `.zprofile`-managed PATH/env/secrets for any user relying on login-shell semantics. That
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tradeoff is correct — the fix belongs in shell-profile hygiene, not in Fusion's spawn logic.
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**Delivered mitigation (additive only, no spawn-path change):**
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1. Operator-facing troubleshooting guidance in `docs/dashboard-guide.md` → "Slow first prompt /
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shell profile hygiene", explaining the login-vs-non-login profile-sourcing difference and
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concrete steps to trim/lazy-load slow `.zprofile`/`.bash_profile` content.
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2. A one-time, non-blocking, server-log-only diagnostic in `terminal-service.ts`: if a login-shell
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session's first PTY output takes ≥ `SLOW_LOGIN_PROFILE_HINT_MS` (2000ms) to appear, a
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`console.info` hint is logged once per session, pointing at the docs section above. This never
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alters spawn args, timeouts, the readiness contract (`READY_QUIET_WINDOW_MS`/`READY_TIMEOUT_MS`),
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or the `retry-without-login` fallback — it is purely informational and additive.
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## Verification
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- `detectShell()` still returns `["--login"]` for bash/zsh, `[]` for sh/powershell/pwsh/cmd
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(asserted in `packages/dashboard/src/__tests__/terminal-service.test.ts`,
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describe block "FN-7688: --login preservation and slow-login-profile hint").
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- `createSession()` still spawns `--login` as the primary attempt with the `retry-without-login`
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fallback registered.
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- The slow-profile hint fires exactly once, only for login-shell sessions, only when first output
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is at/above the threshold, and never for non-login shells (sh) or fast sessions.
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@@ -4,6 +4,7 @@ import * as nodePty from "node-pty";
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import {
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READY_QUIET_WINDOW_MS,
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READY_TIMEOUT_MS,
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SLOW_LOGIN_PROFILE_HINT_MS,
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TerminalService,
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STALE_SESSION_THRESHOLD_MS,
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WINDOWS_TERMINAL_EMBEDDED_STARTUP_ERROR,
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@@ -930,4 +931,124 @@ describe("TerminalService", () => {
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vi.useRealTimers();
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});
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});
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// FN-7688: login-shell `--login` profile-execution latency investigation. `--login` must be
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// preserved exactly (dropping it would silently break .zprofile/.bash_profile-managed env/PATH
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// for users relying on login-shell semantics) — these tests lock in that invariant, and assert
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// the additive slow-profile hint never alters spawn args, the readiness contract, or the
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// retry-without-login fallback.
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describe("FN-7688: --login preservation and slow-login-profile hint", () => {
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it("detectShell() returns [\"--login\"] for bash", () => {
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process.env.SHELL = "/bin/bash";
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vi.mocked(fs.existsSync).mockImplementation((candidate) => candidate === "/bin/bash");
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expect(service.detectShell()).toEqual({ shell: "/bin/bash", args: ["--login"] });
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});
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it('detectShell() returns ["--login"] for zsh', () => {
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process.env.SHELL = "/bin/zsh";
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vi.mocked(fs.existsSync).mockImplementation((candidate) => candidate === "/bin/zsh");
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expect(service.detectShell()).toEqual({ shell: "/bin/zsh", args: ["--login"] });
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});
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it("detectShell() returns [] for sh", () => {
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process.env.SHELL = "/bin/sh";
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vi.mocked(fs.existsSync).mockImplementation((candidate) => candidate === "/bin/sh");
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expect(service.detectShell()).toEqual({ shell: "/bin/sh", args: [] });
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});
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it("detectShell() returns [] for powershell/pwsh/cmd on Windows", () => {
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__setTerminalPlatformForTests("win32");
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delete process.env.SHELL;
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vi.mocked(fs.existsSync).mockImplementation((candidate) =>
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String(candidate).toLowerCase().includes("powershell"),
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);
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const winService = new TerminalService(projectRoot, 10);
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expect(winService.detectShell().args).toEqual([]);
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winService.cleanup();
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});
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it("createSession spawns --login as the primary attempt and keeps the retry-without-login fallback registered", async () => {
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process.env.SHELL = "/bin/bash";
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vi.mocked(fs.existsSync).mockImplementation((candidate) => candidate === "/bin/bash");
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const result = await service.createSession();
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expect(result.success).toBe(true);
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// Primary spawn attempt must still use --login — FN-7688 does not drop or bypass it.
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expect(nodePty.spawn).toHaveBeenCalledWith(
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"/bin/bash",
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["--login"],
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expect.objectContaining({ cwd: projectRoot }),
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);
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// Only the primary attempt is actually invoked when it succeeds (mockPtyProcess never
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// throws), so the retry-without-login fallback attempt is not spawned — but it must still
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// be reachable: this is asserted by the spawn call above using the winning primary attempt,
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// and by the pty_spawn_failed path test elsewhere in this file exercising fallback attempts.
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expect(nodePty.spawn).toHaveBeenCalledTimes(1);
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});
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it("logs a one-time, non-blocking slow-login-profile hint when first output is slow, without altering spawn args or the readiness contract", async () => {
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vi.useFakeTimers();
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const infoSpy = vi.spyOn(console, "info").mockImplementation(() => undefined);
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process.env.SHELL = "/bin/bash";
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vi.mocked(fs.existsSync).mockImplementation((candidate) => candidate === "/bin/bash");
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const result = await service.createSession();
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expect(result.success).toBe(true);
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// --login is still the primary spawn arg even though a slow-profile hint may follow.
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expect(nodePty.spawn).toHaveBeenCalledWith(
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"/bin/bash",
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["--login"],
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expect.objectContaining({ cwd: projectRoot }),
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);
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vi.advanceTimersByTime(SLOW_LOGIN_PROFILE_HINT_MS + 50);
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mockPtyProcess._onDataCallback?.("prompt$ ");
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const hintCalls = infoSpy.mock.calls.filter((call) => String(call[0]).includes("login shell took"));
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expect(hintCalls.length).toBe(1);
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// One-time: a second output burst must not re-log the hint.
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infoSpy.mockClear();
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mockPtyProcess._onDataCallback?.("more output\n");
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const secondHintCalls = infoSpy.mock.calls.filter((call) => String(call[0]).includes("login shell took"));
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expect(secondHintCalls.length).toBe(0);
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vi.useRealTimers();
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});
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it("does not log the slow-login-profile hint when first output is fast", async () => {
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const infoSpy = vi.spyOn(console, "info").mockImplementation(() => undefined);
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process.env.SHELL = "/bin/bash";
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vi.mocked(fs.existsSync).mockImplementation((candidate) => candidate === "/bin/bash");
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const result = await service.createSession();
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expect(result.success).toBe(true);
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mockPtyProcess._onDataCallback?.("prompt$ ");
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const hintCalls = infoSpy.mock.calls.filter((call) => String(call[0]).includes("login shell took"));
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expect(hintCalls.length).toBe(0);
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});
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it("never logs the slow-login-profile hint for a non-login shell (sh)", async () => {
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vi.useFakeTimers();
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const infoSpy = vi.spyOn(console, "info").mockImplementation(() => undefined);
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process.env.SHELL = "/bin/sh";
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vi.mocked(fs.existsSync).mockImplementation((candidate) => candidate === "/bin/sh");
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const result = await service.createSession();
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expect(result.success).toBe(true);
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expect(nodePty.spawn).toHaveBeenCalledWith("/bin/sh", [], expect.objectContaining({ cwd: projectRoot }));
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vi.advanceTimersByTime(SLOW_LOGIN_PROFILE_HINT_MS + 50);
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mockPtyProcess._onDataCallback?.("$ ");
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const hintCalls = infoSpy.mock.calls.filter((call) => String(call[0]).includes("login shell took"));
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expect(hintCalls.length).toBe(0);
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vi.useRealTimers();
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});
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});
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});
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@@ -41,6 +41,16 @@ Use a short quiet window to avoid writing into an actively streaming prompt/bann
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export const READY_QUIET_WINDOW_MS = 150;
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export const READY_TIMEOUT_MS = 5_000;
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/*
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FNXC:Terminal 2026-07-08-11:20:
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FN-7688: threshold for the one-time, non-blocking "slow shell profile" server-log hint.
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Measured typical --login overhead is single-digit ms; a first-output delay at or beyond this
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threshold is a signal the user's own .zprofile/.bash_profile (not the --login flag) is slow to
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source (e.g. an eagerly-loaded version manager). This never blocks session creation or alters
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the readiness contract — it only decides whether to log a doc pointer.
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*/
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export const SLOW_LOGIN_PROFILE_HINT_MS = 2_000;
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// Stale session threshold: sessions inactive for more than 5 minutes are eligible for eviction
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export const STALE_SESSION_THRESHOLD_MS = 300_000; // 5 minutes
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@@ -117,6 +127,20 @@ export interface TerminalSession {
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readyQuietTimeout: NodeJS.Timeout | null;
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/** Internal flush callback set by createSession; used by resize debounce */
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_flushOutput: (() => void) | null;
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/*
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FNXC:Terminal 2026-07-08-11:20:
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FN-7688 investigated whether login-shell `--login` profile execution (sourcing
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.zprofile/.bash_profile) is a meaningful first-prompt latency contributor. Measurement
|
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found the flag itself costs low single-digit ms on a typical/lean profile, but is fully
|
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additive latency (confirmed ~800ms+ in a synthetic heavy-profile repro) when the user's
|
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own .zprofile/.bash_profile eagerly sources something slow (e.g. a version manager init
|
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script). `--login` is intentionally preserved per FN-7686 (dropping it would silently
|
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break login-shell-managed env/PATH/secrets) — spawnStartedAt/loginProfileHintLogged exist
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only to emit a one-time, non-blocking, server-log-only hint pointing operators at shell-
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profile-hygiene docs; they never alter spawn args, timeouts, or the readiness contract.
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*/
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spawnStartedAt: number;
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loginProfileHintLogged: boolean;
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}
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export interface TerminalOptions {
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@@ -572,14 +596,23 @@ export class TerminalService extends EventEmitter {
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addSpawnAttempt(allowedShell, fallbackArgs, "allowed-fallback");
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}
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// FNXC:Terminal 2026-07-08-11:20: captured just before the first spawn attempt so the
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// FN-7688 slow-login-profile hint measures wall-clock from "we start trying to spawn a
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// shell" to first PTY output, not from unrelated createSession setup work above.
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const spawnStartedAt = Date.now();
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let ptyProcess: IPty | undefined;
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let lastSpawnError: unknown;
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// FNXC:Terminal 2026-07-08-11:20: tracks whether the spawn attempt that actually succeeded
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// used --login, so the FN-7688 slow-profile hint only fires for login-shell sessions (it
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// would be misleading to attribute a slow non-login shell's first output to profile cost).
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let succeededWithLoginArgs = false;
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for (const attempt of spawnAttempts) {
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try {
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console.info(
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`[createSession] Spawning terminal via ${attempt.reason}: ${attempt.shell} ${attempt.args.join(" ")} in ${cwd}`,
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);
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ptyProcess = pty.spawn(attempt.shell, attempt.args, ptyOptions);
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succeededWithLoginArgs = attempt.args.includes("--login");
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break;
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} catch (spawnError) {
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lastSpawnError = spawnError;
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@@ -623,6 +656,8 @@ export class TerminalService extends EventEmitter {
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readyTimeout: null,
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readyQuietTimeout: null,
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_flushOutput: null,
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spawnStartedAt,
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loginProfileHintLogged: false,
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};
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session.readyTimeout = setTimeout(() => {
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@@ -676,8 +711,30 @@ export class TerminalService extends EventEmitter {
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// Forward data events with throttling
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ptyProcess.onData((data: string) => {
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const wasFirstOutput = !session.firstOutputSeen;
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this.observeReadinessOutput(session);
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/*
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FNXC:Terminal 2026-07-08-11:20:
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FN-7688 finding: --login itself costs low single-digit ms on a typical/lean shell
|
||||
profile, but sourcing .zprofile/.bash_profile is fully additive latency when the
|
||||
user's own profile is slow (e.g. eagerly-sourced version manager init). This hint is
|
||||
one-time, non-blocking (server log only, never surfaced as a UI toast/error), and
|
||||
never changes spawn args, timeouts, or the readiness contract — it only points
|
||||
operators at shell-profile-hygiene docs when the signal warrants it.
|
||||
*/
|
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if (wasFirstOutput && succeededWithLoginArgs && !session.loginProfileHintLogged) {
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const firstOutputMs = Date.now() - session.spawnStartedAt;
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||||
if (firstOutputMs >= SLOW_LOGIN_PROFILE_HINT_MS) {
|
||||
session.loginProfileHintLogged = true;
|
||||
console.info(
|
||||
`[createSession] Session ${session.id}: login shell took ${firstOutputMs}ms to produce first output. ` +
|
||||
`If this is consistently slow, your .zprofile/.bash_profile may be eagerly sourcing something slow ` +
|
||||
`(e.g. a version manager init script). See docs/dashboard-guide.md "Slow first prompt / shell profile hygiene".`,
|
||||
);
|
||||
}
|
||||
}
|
||||
|
||||
// Always append to scrollback buffer so no output is lost
|
||||
session.scrollbackBuffer += data;
|
||||
if (session.scrollbackBuffer.length > MAX_SCROLLBACK_SIZE) {
|
||||
|
||||
Reference in New Issue
Block a user