pi: apply omp patches via prePatch (bun2nix.hook overrides patchPhase)

`bun2nix.hook` (used by upstream omp's package.nix) sets

  patchPhase = bunPatchPhase

at the end of its setup-hook unless `dontUseBunPatch` is already set.
`bunPatchPhase` only runs `patchShebangs` plus a HOME mktemp; it never
iterates over `$patches`. The standard nixpkgs `patches` attribute
therefore went into the derivation env but was silently ignored at
build time, leaving the deployed omp binary unpatched.

Switch to applying the two patches via `prePatch` (which `bunPatchPhase`
does call). Verified with strings(1) over the rebuilt binary that both
patch hunks land:

  /wrong_api_format|...|invalid tool parameters/  (patch 0001)
  stubsReasoningContent ... thinkingFormat == "openrouter"  (patch 0002)

home/progs/pi.nix

@@ -37,17 +37,21 @@ let
 in
 {
   home.packages = [
+    # `bun2nix.hook` sets `patchPhase = bunPatchPhase`, which only runs `patchShebangs` and
+    # silently ignores the standard `patches` attribute. Apply patches via `prePatch` instead
+    # so they actually take effect. Tracking: nothing upstream yet.
     (inputs.llm-agents.packages.${pkgs.stdenv.hostPlatform.system}.omp.overrideAttrs (old: {
-      patches = (old.patches or [ ]) ++ [
-        # Retry without strict tools when DeepSeek (via OpenRouter) rejects strict-mode `anyOf`
-        # nullable unions with `Invalid tool parameters schema : field \`anyOf\`: missing field \`type\``.
-        # Upstream PR: pending; applies cleanly against v14.2.1.
-        ../../patches/omp/0001-openai-completions-retry-without-strict-on-deepseek-openrouter.patch
-        # Stub `reasoning_content` on tool-call assistant messages for OpenRouter reasoning models.
-        # Fixes DeepSeek V4 Pro et al. rejecting follow-up requests with `400 The \`reasoning_content\`
-        # in the thinking mode must be passed back to the API`. Mirrors the existing Kimi handling.
-        ../../patches/omp/0002-openai-completions-stub-reasoning-content-for-openrouter.patch
-      ];
+      prePatch =
+        (old.prePatch or "")
+        + ''
+          # 0001 — retry without strict tools when DeepSeek (via OpenRouter) rejects strict-mode
+          #        `anyOf` nullable unions with `Invalid tool parameters schema : field \`anyOf\`:
+          #        missing field \`type\``.
+          patch -p1 < ${../../patches/omp/0001-openai-completions-retry-without-strict-on-deepseek-openrouter.patch}
+          # 0002 — require `reasoning_content` for OpenRouter reasoning models so DeepSeek V4 Pro
+          #        et al. accept follow-up requests in thinking mode.
+          patch -p1 < ${../../patches/omp/0002-openai-completions-stub-reasoning-content-for-openrouter.patch}
+        '';
     }))
   ];