diff --git a/CHANGELOG.md b/CHANGELOG.md
index 01d60ea0b0..57307701a8 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -21,6 +21,7 @@
 
 ### 🐛 Bug Fixes
 
+- **fix(headroom):** detect a python interpreter managed by **mise / pyenv / asdf / conda**. Headroom's python probe (`src/lib/headroom/detect.ts`) searched a hardcoded `PATH`, but version managers expose their interpreters via shim dirs that only join `PATH` through interactive-shell activation — which the non-interactive server never runs, so a managed python (≥3.10) was invisible and Headroom reported it missing. The search path now prepends the well-known shim/bin dirs (`~/.local/share/mise/shims`, `~/.pyenv/shims`, `~/.asdf/shims`, `$CONDA_PREFIX/bin`, `~/.local/bin`, respecting `MISE_DATA_DIR`/`PYENV_ROOT`/`ASDF_DATA_DIR` when set), and a new `HEADROOM_PYTHON` env override lets operators point straight at their interpreter (mirroring `HEADROOM_URL`). Still shell-free (`execFileSync`). Regression guard: `tests/unit/headroom-detect.test.ts` (5). (thanks @loopyd)
 - **fix(executors):** strip the OpenAI-Codex/Claude-CLI `client_metadata` passthrough field for **NVIDIA** requests. NVIDIA's OpenAI-compatible wrapper rejects it with `400 Unsupported parameter`, the same class already handled for `cerebras`/`mistral`; `nvidia` (executor `default`) was missing from the strip allowlist so Codex/Claude-Code passthrough requests 400'd. Regression guard: `tests/unit/executor-default-strip-client-metadata.test.ts` (+nvidia case). (thanks @phidinhmanh)
 - **fix(translator):** strip the Claude-style `thinking` field for **NVIDIA `z-ai/glm-5.2`**. NVIDIA's OpenAI-compatible wrapper 400s on `thinking` (a Claude-format client routed here leaves a `thinking:{type:"adaptive"}`); the existing strip rule only dropped `reasoning`. Same class already handled for `minimax-m2.7`. Regression guard: `tests/unit/nvidia-minimax-thinking-strip.test.ts` (+glm-5.2 case). (thanks @phidinhmanh)
 - **fix(translator):** suppress the streamed `</think>` close marker for the **Antigravity IDE** client. On thinking-only turns Antigravity rendered a bare `</think>` as the sole visible content, tripping its loop-detection and wasting requests. Antigravity's UA (`vscode/<v> (Antigravity/<v>)`) is added to the marker-suppress allowlist (alongside OpenCode); Claude Code / Cursor still get the marker, and `x-omniroute-thinking-marker: on` force-restores it. Regression guard: `tests/unit/think-close-marker-suppress-5245.test.ts`. (thanks @abdofallah)
diff --git a/src/lib/headroom/detect.ts b/src/lib/headroom/detect.ts
index cbdd9dd240..7952908e4a 100644
--- a/src/lib/headroom/detect.ts
+++ b/src/lib/headroom/detect.ts
@@ -18,9 +18,8 @@
 import { execFileSync } from "node:child_process";
 
 const EXTRA_BINS = ["/usr/local/bin", "/opt/homebrew/bin", "/usr/bin", "/bin"];
-const EXTENDED_PATH = [...EXTRA_BINS, process.env.PATH || ""].filter(Boolean).join(":");
 
-const PYTHON_CANDIDATES = [
+export const PYTHON_CANDIDATES = [
   "python3.13",
   "python3.12",
   "python3.11",
@@ -28,6 +27,52 @@ const PYTHON_CANDIDATES = [
   "python3",
   "python",
 ];
+
+type EnvLike = Record<string, string | undefined>;
+
+/**
+ * Build the PATH used to locate a python interpreter (upstream 9router#2353).
+ *
+ * Version managers (mise, pyenv, asdf) and conda expose their interpreters via
+ * shim dirs that are only added to PATH by interactive-shell activation
+ * (`eval "$(mise activate bash)"` in `.bashrc`). The non-interactive server
+ * process never runs that, so it would only ever see the system python. We
+ * therefore prepend the well-known shim/bin dirs (respecting the managers' own
+ * root env vars when set) so `findPython310` can discover a managed interpreter.
+ *
+ * Pure + env-injectable so it is unit-testable without spawning.
+ */
+export function buildPythonSearchPath(env: EnvLike = process.env): string {
+  const home = env.HOME || "";
+  const managerDirs: string[] = [];
+  if (home || env.MISE_DATA_DIR) {
+    managerDirs.push(`${env.MISE_DATA_DIR || `${home}/.local/share/mise`}/shims`);
+  }
+  if (home || env.PYENV_ROOT) {
+    managerDirs.push(`${env.PYENV_ROOT || `${home}/.pyenv`}/shims`);
+  }
+  if (home || env.ASDF_DATA_DIR) {
+    managerDirs.push(`${env.ASDF_DATA_DIR || `${home}/.asdf`}/shims`);
+  }
+  if (env.CONDA_PREFIX) {
+    managerDirs.push(`${env.CONDA_PREFIX}/bin`);
+  }
+  if (home) {
+    managerDirs.push(`${home}/.local/bin`); // pipx / uv installs
+  }
+  return [...managerDirs, ...EXTRA_BINS, env.PATH || ""].filter(Boolean).join(":");
+}
+
+/**
+ * Resolve the ordered list of python commands to probe. A `HEADROOM_PYTHON`
+ * override (absolute path or command name) is tried first, mirroring the
+ * `HEADROOM_URL` escape hatch, so operators on exotic setups can point directly
+ * at their interpreter (upstream 9router#2353).
+ */
+export function resolvePythonCandidates(env: EnvLike = process.env): string[] {
+  const override = env.HEADROOM_PYTHON?.trim();
+  return override ? [override, ...PYTHON_CANDIDATES] : [...PYTHON_CANDIDATES];
+}
 const MIN_VERSION: readonly [number, number] = [3, 10];
 const HEADROOM_HEALTH_TIMEOUT_MS = 1500;
 const LOOPBACK_HOSTS = new Set(["localhost", "127.0.0.1", "::1", "[::1]", "0.0.0.0"]);
@@ -106,7 +151,7 @@ export function findHeadroomBinary(): string | null {
     const out = execFileSync("which", ["headroom"], {
       stdio: ["ignore", "pipe", "ignore"],
       windowsHide: true,
-      env: { ...process.env, PATH: EXTENDED_PATH },
+      env: { ...process.env, PATH: buildPythonSearchPath() },
     })
       .toString()
       .trim();
@@ -117,14 +162,16 @@ export function findHeadroomBinary(): string | null {
 }
 
 export function findPython310(): string | null {
-  for (const candidate of PYTHON_CANDIDATES) {
+  const searchPath = buildPythonSearchPath();
+  for (const candidate of resolvePythonCandidates()) {
     try {
-      // candidate is from a fixed allowlist (PYTHON_CANDIDATES) above — no
-      // user input — but use execFileSync anyway to remove the shell entirely.
+      // candidate is from a fixed allowlist (PYTHON_CANDIDATES) plus an optional
+      // operator-set HEADROOM_PYTHON override — never remote/request input — but
+      // use execFileSync anyway to remove the shell entirely.
       const ver = execFileSync(candidate, ["--version"], {
         stdio: ["ignore", "pipe", "ignore"],
         windowsHide: true,
-        env: { ...process.env, PATH: EXTENDED_PATH },
+        env: { ...process.env, PATH: searchPath },
       })
         .toString()
         .trim();
diff --git a/tests/unit/headroom-detect.test.ts b/tests/unit/headroom-detect.test.ts
new file mode 100644
index 0000000000..1978c59072
--- /dev/null
+++ b/tests/unit/headroom-detect.test.ts
@@ -0,0 +1,58 @@
+import { test } from "node:test";
+import assert from "node:assert/strict";
+
+import {
+  buildPythonSearchPath,
+  resolvePythonCandidates,
+  PYTHON_CANDIDATES,
+} from "../../src/lib/headroom/detect.ts";
+
+// Regression guard for upstream 9router#2353 — Headroom could not detect a
+// python interpreter managed by mise / pyenv / conda because those tools only
+// add their shim dirs to PATH via interactive-shell activation, which the
+// non-interactive server process never runs.
+
+test("buildPythonSearchPath includes env-manager shim dirs derived from HOME", () => {
+  const path = buildPythonSearchPath({ HOME: "/home/dev", PATH: "/usr/bin" });
+  const segments = path.split(":");
+  assert.ok(segments.includes("/home/dev/.local/share/mise/shims"), "mise shims");
+  assert.ok(segments.includes("/home/dev/.pyenv/shims"), "pyenv shims");
+  assert.ok(segments.includes("/home/dev/.asdf/shims"), "asdf shims");
+  assert.ok(segments.includes("/home/dev/.local/bin"), "user local bin (pipx/uv)");
+  // still preserves the caller's PATH and the classic EXTRA_BINS
+  assert.ok(segments.includes("/usr/bin"), "inherited PATH preserved");
+  assert.ok(segments.includes("/opt/homebrew/bin"), "homebrew bin preserved");
+});
+
+test("buildPythonSearchPath honors CONDA_PREFIX and custom manager roots", () => {
+  const path = buildPythonSearchPath({
+    HOME: "/home/dev",
+    CONDA_PREFIX: "/opt/conda/envs/ml",
+    PYENV_ROOT: "/custom/pyenv",
+    MISE_DATA_DIR: "/custom/mise",
+  });
+  const segments = path.split(":");
+  assert.ok(segments.includes("/opt/conda/envs/ml/bin"), "active conda env bin");
+  assert.ok(segments.includes("/custom/pyenv/shims"), "PYENV_ROOT override");
+  assert.ok(segments.includes("/custom/mise/shims"), "MISE_DATA_DIR override");
+});
+
+test("buildPythonSearchPath is robust when HOME/PATH are absent", () => {
+  const path = buildPythonSearchPath({});
+  const segments = path.split(":").filter(Boolean);
+  // no empty segments, still returns the static EXTRA_BINS
+  assert.ok(segments.includes("/usr/bin"));
+  assert.ok(!path.includes("::"), "no empty path segments");
+});
+
+test("resolvePythonCandidates puts HEADROOM_PYTHON override first", () => {
+  const candidates = resolvePythonCandidates({ HEADROOM_PYTHON: "/opt/py/bin/python" });
+  assert.equal(candidates[0], "/opt/py/bin/python");
+  // default candidates still follow
+  assert.ok(candidates.includes("python3"));
+});
+
+test("resolvePythonCandidates returns the default list when no override", () => {
+  const candidates = resolvePythonCandidates({});
+  assert.deepEqual(candidates, [...PYTHON_CANDIDATES]);
+});