fix(headless): S1 ACDREAM_HEADLESS_CONSOLE=0 disables even on a real terminal

HeadlessConsoleOptions.Resolve tested the environment variable against
the literal "1", so ACDREAM_HEADLESS_CONSOLE=0 silently fell through to
the terminal-shaped default (on when stdin is a real console) instead of
acting as an A/B off-switch. Now: once the variable is SET AT ALL, any
value other than "0" enables and "0" disables -- the same idiom
ACDREAM_RETAIL_CLOSE_DEGRADES / ACDREAM_RETAIL_UI already use. An unset
variable still falls through to the terminal default.

Registered the flag as the sixth entry in
LaunchOptionsDocumentationTests.DefaultOnBehaviorFlags and updated the
Conventions section of docs/launch-options.md plus the flag's own row
(side-effects column corrected to describe the real precedence).

ResolvePrefersFlagThenEnvironmentThenTerminalDefault's env="0"/terminal
=true case was shown to fail against the prior `== "1"` implementation
(expected false, old code returned true) before the fix landed; the
env="yes" case also failed on the same mutation (old code required the
literal "1", so "yes" fell through to terminal=false instead of enabling).

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

docs/launch-options.md

@@ -40,12 +40,16 @@ Assume a flag has a side effect until its row says otherwise.
 - **Everything diagnostic is OFF by default.** Every probe, dump, capture,
   and measurement flag in this document is inert until its variable is
   explicitly set — an unset environment runs zero diagnostics. Exactly
-  five flags default ON, and none is a diagnostic: `ACDREAM_RETAIL_CHASE`,
+  six flags default ON, and none is a diagnostic: `ACDREAM_RETAIL_CHASE`,
   `ACDREAM_CAMERA_COLLIDE`, `ACDREAM_CAMERA_ALIGN_SLOPE`, and
   `ACDREAM_RETAIL_CLOSE_DEGRADES` are retail *behaviors* wearing an A/B
   off-switch (`=0` disables the behavior for a comparison run), while
   `ACDREAM_RETAIL_UI` is the product's only gameplay presentation and uses
-  the same explicit diagnostic opt-out. That five-flag set is frozen by
+  the same explicit diagnostic opt-out. `ACDREAM_HEADLESS_CONSOLE` is the
+  sixth: its unset default is terminal-shaped (on when stdin is a real
+  console, off when redirected — not unconditionally on like the other
+  five), but once the variable is SET AT ALL it uses the identical `=0`
+  override (any other value enables). That six-flag set is frozen by
   `LaunchOptionsDocumentationTests` — a new
   default-on flag fails the build.
 - `=1` means the code tests for exactly the string `1`. Setting `true`,
@@ -93,7 +97,7 @@ dotnet run --project src\AcDream.App\AcDream.App.csproj --no-build -c Release
 | `ACDREAM_DAT_DIR` | `=<path>` | Fallback dat-directory when no positional argument is given. App: single read at `Program.cs:58`. Cli: read independently per-subcommand (each subcommand does `args.ElementAtOrDefault(N) ?? Env.GetEnvironmentVariable("ACDREAM_DAT_DIR")`) plus once more for the default (no-subcommand) asset-inventory mode at line 152. | Two of the four `Program.cs` line numbers in the raw grep (91, 135) are **not reads** — they're the literal string `ACDREAM_DAT_DIR` inside `Log.Error` usage-text messages, not `GetEnvironmentVariable` calls. Only line 58 is a real read in `AcDream.App`. | none — hard usage error (exit 2) if unset and no positional arg | `Program.cs:58` (App); `Cli/Program.cs:24,35,47,59,71,84,113,125,137,152` (every Cli subcommand) |
 | `ACDREAM_DISPLAY_PROTOCOL` | `="auto"` / `"x11"` / `"wayland"` (case-insensitive, trimmed); any other value throws `InvalidOperationException` at startup | Linux-only: forces the GLFW 3.4 platform-init hint (X11 vs Wayland vs auto) before any window is created; ignored entirely on Windows (always `Windows` protocol) | An invalid value is fatal at startup (throws before any window exists), not a silent fallback | unset → auto-detected from `XDG_SESSION_TYPE`/`WAYLAND_DISPLAY`/`DISPLAY`, falling back to GLFW `Automatic` | `GraphicalWindowBackendSelection.Resolve` (`GraphicalWindowBackendSelection.cs:26-58`) |
 | `ACDREAM_FAR_RADIUS` | `=<int>` | Overrides preset's `FarRadius` (outer streaming/reveal window, landblocks) | Enlarging changes streaming memory budget and what's resident/rendered — CLAUDE.md: leave unset for measurement/gate runs (same family as legacy `ACDREAM_STREAM_RADIUS`) | preset's `FarRadius` (Low=5, Medium=8, High=12, Ultra=15) | `QualitySettings.WithEnvOverrides` (`QualityPreset.cs:47`) |
-| `ACDREAM_HEADLESS_CONSOLE` | `=1` enables | Turns on the headless host's interactive console (docs/plans/2026-09-07-headless-console.md): a background thread reads stdin lines, each drained on the session tick through the SAME plugin-verb/client-slash-command pipeline the graphical chat box uses, with chat/lifecycle/portal output rendered to stdout. Only takes effect for `run` with a single configured session — the launcher's multi-session mode is unaffected. | Starts a background stdin-reader thread and writes plain-text lines to the same stdout stream `HeadlessDiagnosticWriter` already uses for its JSON lines — the two interleave. Only applies to `run`; `--console` (bare flag, no value) always wins over this variable, which in turn always wins over the terminal-shaped default. | unset → on when stdin is a real console, off when redirected (`!Console.IsInputRedirected`, checked once in `Program.cs`) | `HeadlessConsoleOptions.Resolve` (`Configuration/HeadlessConsoleOptions.cs`) → `HeadlessEntryPoint.Run` → `HeadlessProcessHost`'s `consoleEnabled` |
+| `ACDREAM_HEADLESS_CONSOLE` | `=0` disables (once set at all); any other value enables; unset falls through to the terminal-shaped default | Turns on the headless host's interactive console (docs/plans/2026-09-07-headless-console.md): a background thread reads stdin lines, each drained on the session tick through the SAME plugin-verb/client-slash-command pipeline the graphical chat box uses, with chat/lifecycle/portal output rendered to stdout. Only takes effect for `run` with a single configured session — a multi-session process reports `console: single-session only` via the diagnostics stream and does not attach one. | Starts a background stdin-reader thread and writes plain-text lines to the same stdout stream `HeadlessDiagnosticWriter` already uses for its JSON lines — the two interleave. Only applies to `run`; `--console` (bare flag, no value) always wins over this variable. S1 fix (2026-09-07): the variable itself now wins outright once SET AT ALL — `=0` disables even when stdin is a real terminal, matching every other `=0`-disables flag in this table; only an UNSET variable falls through to the terminal-shaped default. | unset → on when stdin is a real console, off when redirected (`!Console.IsInputRedirected`, checked once in `Program.cs`); set → `!= "0"` | `HeadlessConsoleOptions.Resolve` (`Configuration/HeadlessConsoleOptions.cs`) → `HeadlessEntryPoint.Run` → `HeadlessProcessHost`'s `consoleEnabled` |
 | `ACDREAM_LIVE` | `=1` (exactly the literal string `"1"`) | Core switch: connect to a live ACE server instead of running offline/no-connect. | The 4 non-`RuntimeOptions.cs` line numbers in the raw grep are **all comments or log-message text**, not reads — `SessionStartComposition.cs:39` is inside the string `"live: ACDREAM_LIVE set but TEST_USER/TEST_PASS missing; skipping"`; `Program.cs:126` is inside a `--session-config` override log line; `GameWindow.cs:614,627` are doc comments. The only actual parse is `RuntimeOptions.cs:141`. Requires `ACDREAM_TEST_USER`/`ACDREAM_TEST_PASS` too (`HasLiveCredentials`) or the session silently reports `MissingCredentials` and skips. Forced to effectively-on (LiveMode=true) unconditionally by `--session-config` launches regardless of this var. | `false` | `RuntimeOptions.LiveMode` → `SessionStartComposition.cs` (log text only), `Program.cs:126` (log text only), `GameWindow.cs:614,627` (comments only), consumed for real via `RuntimeOptions.HasLiveCredentials` and `WorldSession`/`GameRuntime` session-start gating |
 | `ACDREAM_MAX_COMPLETIONS_PER_FRAME` | `=<int>` | Overrides preset's per-frame streaming-completion throughput cap | Directly changes the streaming admission budget measured by perf/completion gates — do not vary during a measurement run | preset's value (Low=2, Medium=3, High=4, Ultra=6) | `QualitySettings.WithEnvOverrides` (`QualityPreset.cs:59`) |
 | `ACDREAM_MSAA_SAMPLES` | `=<int>` (0/2/4/8) | Overrides preset's MSAA sample count | Changes GPU multisample anti-aliasing (visual + GPU-cost change) | preset's `MsaaSamples` (Low=0, Medium=2, High/Ultra=4) | `QualitySettings.WithEnvOverrides` (`QualityPreset.cs:48`) |

src/AcDream.Headless/Configuration/HeadlessConsoleOptions.cs

@@ -4,13 +4,24 @@ namespace AcDream.Headless.Configuration;
 /// Typed resolution for the headless interactive console (docs/plans/
 /// 2026-09-07-headless-console.md). Three inputs, first match wins:
 /// the <c>--console</c> command-line flag, the
-/// <c>ACDREAM_HEADLESS_CONSOLE=1</c> environment variable, and finally a
+/// <c>ACDREAM_HEADLESS_CONSOLE</c> environment variable, and finally a
 /// terminal-shaped default — on when stdin is a real console (an operator
 /// typing at a keyboard), off when it is redirected (a script, CI runner, or
 /// piped fixture, where a background reader thread blocked on
 /// <c>ReadLine</c> would never see input and would just sit idle). See
 /// docs/launch-options.md for the documented row this owns.
 /// </summary>
+/// <remarks>
+/// S1 fix (2026-09-07 review round): the environment variable is a
+/// default-on override once it is SET at all, not a bare "equals 1" test —
+/// <c>ACDREAM_HEADLESS_CONSOLE=0</c> must disable the console even when
+/// stdin is a real terminal, matching the
+/// <c>ACDREAM_RETAIL_CLOSE_DEGRADES</c> / <c>ACDREAM_RETAIL_UI</c>
+/// convention (any value other than the literal string <c>"0"</c> enables).
+/// An UNSET variable still falls through to the terminal-shaped default —
+/// this flag's "default on" is conditional on stdin, unlike those two, but
+/// once set at all it behaves identically.
+/// </remarks>
 internal static class HeadlessConsoleOptions
 {
     internal const string EnvironmentVariable = "ACDREAM_HEADLESS_CONSOLE";
@@ -25,14 +36,18 @@ internal static class HeadlessConsoleOptions
 
     internal static bool Resolve(
         bool commandLineFlag,
-        Func<string, string?> environment,
+        Func<string, string?> env,
         bool standardInputIsTerminal)
     {
-        ArgumentNullException.ThrowIfNull(environment);
+        ArgumentNullException.ThrowIfNull(env);
         if (commandLineFlag)
             return true;
-        if (environment(EnvironmentVariable) == "1")
-            return true;
-        return standardInputIsTerminal;
+        if (env(EnvironmentVariable) is null)
+            return standardInputIsTerminal;
+        // Default-on once the flag is set at all: any value other than the
+        // literal string "0" enables the console — the same
+        // ACDREAM_RETAIL_CLOSE_DEGRADES / ACDREAM_RETAIL_UI idiom.
+        return !string.Equals(
+            env("ACDREAM_HEADLESS_CONSOLE"), "0", StringComparison.Ordinal);
     }
 }

tests/AcDream.App.Tests/Diagnostics/LaunchOptionsDocumentationTests.cs

@@ -107,10 +107,14 @@ public sealed class LaunchOptionsDocumentationTests
     }
 
     /// <summary>
-    /// The five flags that default ON. All are product/retail behaviors wearing an
-    /// A/B off-switch (<c>=0</c> disables) — none is a diagnostic. FROZEN:
-    /// a diagnostic that activates without its env var set taxes every run
-    /// and every measurement silently, so growing this set fails.
+    /// The six flags that default ON. All are product/retail behaviors wearing an
+    /// A/B off-switch (<c>=0</c> disables) — none is a diagnostic.
+    /// <c>ACDREAM_HEADLESS_CONSOLE</c> (added 2026-09-07, S1 fix round) is the
+    /// odd one out: its UNSET default is terminal-shaped, not unconditionally
+    /// on — but once it is SET AT ALL it reads the identical <c>=0</c>-disables
+    /// idiom this regex detects, so it belongs in this set on the same terms.
+    /// FROZEN: a diagnostic that activates without its env var set taxes every
+    /// run and every measurement silently, so growing this set fails.
     /// </summary>
     private static readonly IReadOnlySet<string> DefaultOnBehaviorFlags =
         new HashSet<string>(StringComparer.Ordinal)
@@ -120,6 +124,7 @@ public sealed class LaunchOptionsDocumentationTests
             "ACDREAM_CAMERA_ALIGN_SLOPE",
             "ACDREAM_RETAIL_CLOSE_DEGRADES",
             "ACDREAM_RETAIL_UI",
+            "ACDREAM_HEADLESS_CONSOLE",
         };
 
     /// <summary>
@@ -134,7 +139,7 @@ public sealed class LaunchOptionsDocumentationTests
         RegexOptions.Compiled);
 
     [Fact]
-    public void OnlyTheFiveProductBehaviorFlagsDefaultOn()
+    public void OnlyTheSixProductBehaviorFlagsDefaultOn()
     {
         var defaultOn = new HashSet<string>(StringComparer.Ordinal);
         foreach ((string path, _) in SourceFiles())

tests/AcDream.Headless.Tests/HeadlessConsoleTests.cs

@@ -31,10 +31,16 @@ public sealed class HeadlessConsoleTests
     // ── HeadlessConsoleOptions (typed option resolution) ─────────────────
 
     [Theory]
-    [InlineData(true, "0", false, true)]   // CLI flag always wins
-    [InlineData(false, "1", false, true)]  // env var wins over terminal default
-    [InlineData(false, "0", true, true)]   // env var "0" does not disable the terminal default
-    [InlineData(false, null, true, true)]  // no flag/env -> terminal-shaped default (on)
+    [InlineData(true, "0", false, true)]    // CLI flag always wins, even over env "0"
+    [InlineData(false, "1", false, true)]   // env var "1" wins over terminal default
+    [InlineData(false, "yes", false, true)] // any non-"0" env value enables (RETAIL_CLOSE_DEGRADES/RETAIL_UI idiom)
+    // S1 fix (2026-09-07 review round): ACDREAM_HEADLESS_CONSOLE=0 must
+    // disable the console even when stdin IS a real terminal — the earlier
+    // `== "1"` test let "0" silently fall through to the terminal-shaped
+    // default instead of acting as the documented A/B off-switch.
+    [InlineData(false, "0", true, false)]   // env var "0" disables even when stdin is a terminal
+    [InlineData(false, "0", false, false)]  // env var "0" disables when stdin is redirected too
+    [InlineData(false, null, true, true)]   // no flag/env -> terminal-shaped default (on)
     [InlineData(false, null, false, false)] // no flag/env -> terminal-shaped default (off)
     public void ResolvePrefersFlagThenEnvironmentThenTerminalDefault(
         bool commandLineFlag,