diff --git a/.github/actions/build-native/action.yml b/.github/actions/build-native/action.yml
index 00798234d..68398dbcc 100644
--- a/.github/actions/build-native/action.yml
+++ b/.github/actions/build-native/action.yml
@@ -129,8 +129,7 @@ runs:
       - uses: oven-sh/setup-bun@v2
         with:
            bun-version: "1.3"
-      - shell: bash
-        run: bun install --frozen-lockfile
+      - uses: ./.github/actions/bun-install
       # Cross-compile toolchain selection: non-MSVC targets (e.g.
       # `aarch64-unknown-linux-gnu`) build with `cargo-zigbuild`; MSVC targets
       # (e.g. `x86_64-pc-windows-msvc`) build with `cargo-xwin`. The napi CLI's
diff --git a/.github/actions/bun-install/action.yml b/.github/actions/bun-install/action.yml
new file mode 100644
index 000000000..b702e5140
--- /dev/null
+++ b/.github/actions/bun-install/action.yml
@@ -0,0 +1,47 @@
+name: "bun install (shared cache)"
+description: >
+   Run `bun install --frozen-lockfile` with a shared dependency cache. On
+   self-hosted omp-kata runners (where the sccache S3 credentials are injected)
+   the bun store and node_modules are cached in the in-cluster RustFS S3; every
+   other runner falls back to the stock actions/cache backend.
+
+runs:
+   using: composite
+   steps:
+      # The whole repo already keys "are we on hosted infra?" off
+      # $SCCACHE_BUCKET (see actions/build-native). RUNNER_ENVIRONMENT is empty
+      # on ARC pods, so it is not a usable signal here.
+      - name: Detect cache backend
+        id: backend
+        shell: bash
+        run: |
+           if [ -n "${SCCACHE_BUCKET:-}" ] && [ -n "${AWS_ACCESS_KEY_ID:-}" ]; then
+             echo "kind=rustfs" >> "$GITHUB_OUTPUT"
+             echo "bun cache backend: RustFS S3 ($SCCACHE_BUCKET @ $SCCACHE_ENDPOINT)"
+           else
+             echo "kind=gha" >> "$GITHUB_OUTPUT"
+             echo "bun cache backend: GitHub Actions cache"
+           fi
+
+      # Off-infra (GitHub-hosted): stock actions/cache for the bun store.
+      - name: Cache bun store (GitHub cache)
+        if: steps.backend.outputs.kind == 'gha'
+        uses: actions/cache@v4
+        with:
+           path: ~/.bun/install/cache
+           key: bun-${{ runner.os }}-${{ hashFiles('**/bun.lock') }}
+
+      # On-infra (omp-kata): RustFS store + node_modules over the LAN.
+      - name: Restore bun caches (RustFS)
+        if: steps.backend.outputs.kind == 'rustfs'
+        shell: bash
+        run: bash "$GITHUB_ACTION_PATH/rustfs-cache.sh" restore
+
+      - name: Install dependencies
+        shell: bash
+        run: bun install --frozen-lockfile
+
+      - name: Save bun caches (RustFS)
+        if: steps.backend.outputs.kind == 'rustfs'
+        shell: bash
+        run: bash "$GITHUB_ACTION_PATH/rustfs-cache.sh" save
diff --git a/.github/actions/bun-install/rustfs-cache.sh b/.github/actions/bun-install/rustfs-cache.sh
new file mode 100755
index 000000000..4a9cc70a5
--- /dev/null
+++ b/.github/actions/bun-install/rustfs-cache.sh
@@ -0,0 +1,123 @@
+#!/usr/bin/env bash
+# Shared bun dependency cache backed by the in-cluster RustFS (S3) object store.
+#
+# Used by .github/actions/bun-install on the self-hosted omp-kata runners. There
+# the stock `actions/cache` restore of ~/.bun/install/cache costs 130-186s per
+# job because GitHub's cache backend is only reachable over the node's NAT
+# egress, and ~9 jobs contend on it at once. RustFS lives in the same k3s node
+# (svc :9000, already allowed by the runner egress NetworkPolicy), so the same
+# payload moves at LAN speed.
+#
+# Credentials are the ones sccache already gets via the `sccache-s3` secret
+# (envFrom on every runner pod): AWS_ACCESS_KEY_ID / AWS_SECRET_ACCESS_KEY /
+# SCCACHE_ENDPOINT / SCCACHE_BUCKET / SCCACHE_REGION / SCCACHE_S3_USE_SSL.
+#
+# Two objects per lockfile, under the bun-cache/ key prefix of the sccache
+# bucket:
+#   store-<os>-<lockhash>   the bun global package store (~/.bun/install/cache)
+#   nm-<os>-<lockhash>      the installed node_modules trees (root + workspaces)
+# The store additionally publishes a rolling store-<os>-latest alias, so a
+# changed lockfile still warm-starts from the previous store and `bun install`
+# only fetches the delta. A node_modules hit short-circuits everything: the
+# subsequent `bun install --frozen-lockfile` is a no-op, so the store is neither
+# fetched nor saved.
+set -euo pipefail
+
+mode="${1:?usage: rustfs-cache.sh restore|save}"
+
+: "${SCCACHE_BUCKET:?SCCACHE_BUCKET required}"
+: "${SCCACHE_ENDPOINT:?SCCACHE_ENDPOINT required}"
+: "${AWS_ACCESS_KEY_ID:?AWS_ACCESS_KEY_ID required}"
+: "${AWS_SECRET_ACCESS_KEY:?AWS_SECRET_ACCESS_KEY required}"
+
+region="${SCCACHE_REGION:-us-east-1}"
+if [ "${SCCACHE_S3_USE_SSL:-false}" = "true" ]; then scheme=https; else scheme=http; fi
+base="${scheme}://${SCCACHE_ENDPOINT}/${SCCACHE_BUCKET}/bun-cache"
+os="${RUNNER_OS:-$(uname -s)}"
+store_dir="${BUN_INSTALL_CACHE_DIR:-${HOME}/.bun/install/cache}"
+work="${RUNNER_TEMP:-/tmp}/bun-rustfs-cache"
+mkdir -p "$work"
+
+# Prefer multi-threaded zstd (baked into the omp-kata runner image); fall back to
+# gzip so the action still works on an image that predates the zstd addition. The
+# object suffix records the codec, and restore only inflates archives this host
+# can actually decompress.
+if command -v zstd >/dev/null 2>&1; then
+   tar_c=(-I "zstd -3 -T0"); ext="tzst"; alt_ext="tgz"
+else
+   tar_c=(-I "gzip -6"); ext="tgz"; alt_ext="tzst"
+fi
+
+lock_hash="$(sha256sum bun.lock | cut -c1-32)"
+store_key="store-${os}-${lock_hash}"
+store_latest="store-${os}-latest"
+nm_key="nm-${os}-${lock_hash}"
+
+auth=(--aws-sigv4 "aws:amz:${region}:s3" --user "${AWS_ACCESS_KEY_ID}:${AWS_SECRET_ACCESS_KEY}")
+# 404 (-f) and connection errors are non-zero; transient errors retry, 4xx do not.
+s3_get()    { curl -fsS --retry 3 --retry-connrefused "${auth[@]}" "${base}/$1" -o "$2"; }
+s3_exists() { curl -fsS -I --retry 3 --retry-connrefused "${auth[@]}" "${base}/$1" -o /dev/null >/dev/null 2>&1; }
+s3_put()    { curl -fsS --retry 3 --retry-connrefused "${auth[@]}" -T "$2" "${base}/$1" -o /dev/null; }
+
+# Download <name>.<ext> (then the alternate codec) and extract into dir $2.
+# tar auto-detects the codec from the archive; a present-but-uninflatable archive
+# (codec mismatch with this host) is treated as a miss.
+fetch_extract() { # name dest
+   local name="$1" dest="$2" e f
+   for e in "$ext" "$alt_ext"; do
+      f="${work}/${name}.${e}"
+      if s3_get "${name}.${e}" "$f" 2>/dev/null; then
+         mkdir -p "$dest"
+         if tar -xf "$f" -C "$dest" 2>/dev/null; then rm -f "$f"; return 0; fi
+         rm -f "$f"
+      fi
+   done
+   return 1
+}
+
+case "$mode" in
+restore)
+   if fetch_extract "$nm_key" "$PWD"; then
+      echo "bun cache: node_modules HIT ($nm_key) — install becomes a no-op"
+      : > "${work}/nm_hit"
+      exit 0
+   fi
+   echo "bun cache: node_modules miss ($nm_key)"
+   if fetch_extract "$store_key" "$store_dir"; then
+      echo "bun cache: store HIT ($store_key)"
+   elif fetch_extract "$store_latest" "$store_dir"; then
+      echo "bun cache: store warm-start ($store_latest)"
+   else
+      echo "bun cache: store miss — cold install"
+   fi
+   ;;
+save)
+   if [ -f "${work}/nm_hit" ]; then
+      echo "bun cache: node_modules was a hit — nothing to save"
+      exit 0
+   fi
+   # Store (+ rolling latest): save when this exact lockfile has none yet.
+   if [ -d "$store_dir" ] && ! s3_exists "${store_key}.${ext}"; then
+      tar "${tar_c[@]}" -cf "${work}/store.${ext}" -C "$store_dir" .
+      s3_put "${store_key}.${ext}" "${work}/store.${ext}"
+      s3_put "${store_latest}.${ext}" "${work}/store.${ext}"
+      rm -f "${work}/store.${ext}"
+      echo "bun cache: saved store ($store_key + $store_latest)"
+   fi
+   # node_modules: save the installed trees for this exact lockfile.
+   if ! s3_exists "${nm_key}.${ext}"; then
+      shopt -s nullglob
+      nm_paths=(node_modules packages/*/node_modules python/robomp/web/node_modules)
+      if [ ${#nm_paths[@]} -gt 0 ]; then
+         tar "${tar_c[@]}" -cf "${work}/nm.${ext}" "${nm_paths[@]}"
+         s3_put "${nm_key}.${ext}" "${work}/nm.${ext}"
+         rm -f "${work}/nm.${ext}"
+         echo "bun cache: saved node_modules ($nm_key, ${#nm_paths[@]} trees)"
+      fi
+   fi
+   ;;
+*)
+   echo "rustfs-cache.sh: unknown mode '$mode' (want restore|save)" >&2
+   exit 2
+   ;;
+esac
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 566268cea..63693aa25 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -193,12 +193,7 @@ jobs:
          - uses: oven-sh/setup-bun@v2
            with:
               bun-version: "1.3"
-         - name: Cache bun dependencies
-           uses: actions/cache@v4
-           with:
-              path: ~/.bun/install/cache
-              key: bun-${{ runner.os }}-${{ hashFiles('**/bun.lock') }}
-         - run: bun install --frozen-lockfile
+         - uses: ./.github/actions/bun-install
          - name: Type check workspace
            run: bun run ci:check:full
          - name: Build collab web
@@ -267,12 +262,7 @@ jobs:
          - uses: oven-sh/setup-bun@v2
            with:
               bun-version: "1.3"
-         - name: Cache bun dependencies
-           uses: actions/cache@v4
-           with:
-              path: ~/.bun/install/cache
-              key: bun-${{ runner.os }}-${{ hashFiles('**/bun.lock') }}
-         - run: bun install --frozen-lockfile
+         - uses: ./.github/actions/bun-install
          - name: Resolve Linux x64 native artifact run
            id: source
            shell: bash
@@ -304,12 +294,7 @@ jobs:
          - uses: oven-sh/setup-bun@v2
            with:
               bun-version: "1.3"
-         - name: Cache bun dependencies
-           uses: actions/cache@v4
-           with:
-              path: ~/.bun/install/cache
-              key: bun-${{ runner.os }}-${{ hashFiles('**/bun.lock') }}
-         - run: bun install --frozen-lockfile
+         - uses: ./.github/actions/bun-install
          - name: Resolve Linux x64 native artifact run
            id: source
            shell: bash
@@ -343,13 +328,8 @@ jobs:
          - uses: oven-sh/setup-bun@v2
            with:
               bun-version: "1.3"
-         - name: Cache bun dependencies
-           uses: actions/cache@v4
-           with:
-              path: ~/.bun/install/cache
-              key: bun-${{ runner.os }}-${{ hashFiles('**/bun.lock') }}
          - uses: ./.github/actions/setup-system-deps
-         - run: bun install --frozen-lockfile
+         - uses: ./.github/actions/bun-install
          - name: Resolve Linux x64 native artifact run
            id: source
            shell: bash
@@ -381,13 +361,8 @@ jobs:
          - uses: oven-sh/setup-bun@v2
            with:
               bun-version: "1.3"
-         - name: Cache bun dependencies
-           uses: actions/cache@v4
-           with:
-              path: ~/.bun/install/cache
-              key: bun-${{ runner.os }}-${{ hashFiles('**/bun.lock') }}
          - uses: ./.github/actions/setup-system-deps
-         - run: bun install --frozen-lockfile
+         - uses: ./.github/actions/bun-install
          - name: Resolve Linux x64 native artifact run
            id: source
            shell: bash
@@ -419,12 +394,7 @@ jobs:
          - uses: oven-sh/setup-bun@v2
            with:
               bun-version: "1.3"
-         - name: Cache bun dependencies
-           uses: actions/cache@v4
-           with:
-              path: ~/.bun/install/cache
-              key: bun-${{ runner.os }}-${{ hashFiles('**/bun.lock') }}
-         - run: bun install --frozen-lockfile
+         - uses: ./.github/actions/bun-install
          - name: Resolve Linux x64 native artifact run
            id: source
            shell: bash
@@ -458,13 +428,8 @@ jobs:
          - uses: oven-sh/setup-bun@v2
            with:
               bun-version: "1.3"
-         - name: Cache bun dependencies
-           uses: actions/cache@v4
-           with:
-              path: ~/.bun/install/cache
-              key: bun-${{ runner.os }}-${{ hashFiles('**/bun.lock') }}
          - uses: ./.github/actions/setup-system-deps
-         - run: bun install --frozen-lockfile
+         - uses: ./.github/actions/bun-install
          - name: Resolve Linux x64 native artifact run
            id: source
            shell: bash
@@ -496,13 +461,8 @@ jobs:
          - uses: oven-sh/setup-bun@v2
            with:
               bun-version: "1.3"
-         - name: Cache bun dependencies
-           uses: actions/cache@v4
-           with:
-              path: ~/.bun/install/cache
-              key: bun-${{ runner.os }}-${{ hashFiles('**/bun.lock') }}
          - uses: ./.github/actions/setup-system-deps
-         - run: bun install --frozen-lockfile
+         - uses: ./.github/actions/bun-install
          - name: Resolve Linux x64 native artifact run
            id: source
            shell: bash
@@ -561,13 +521,8 @@ jobs:
                 echo "SCCACHE_GHA_ENABLED=true" >> "$GITHUB_ENV"
                 echo "sccache backend: GitHub Actions cache"
               fi
-         - name: Cache bun dependencies
-           uses: actions/cache@v4
-           with:
-              path: ~/.bun/install/cache
-              key: bun-${{ runner.os }}-${{ hashFiles('**/bun.lock') }}
          - uses: ./.github/actions/setup-system-deps
-         - run: bun install --frozen-lockfile
+         - uses: ./.github/actions/bun-install
          - name: Install method smoke tests
            run: bun run ci:test:install-methods
 
diff --git a/packages/coding-agent/src/eval/__tests__/agent-bridge.test.ts b/packages/coding-agent/src/eval/__tests__/agent-bridge.test.ts
index 1c63b3431..d9820ffde 100644
--- a/packages/coding-agent/src/eval/__tests__/agent-bridge.test.ts
+++ b/packages/coding-agent/src/eval/__tests__/agent-bridge.test.ts
@@ -679,13 +679,14 @@ describe("agent() through eval runtimes", () => {
 					cost: 0,
 					durationMs: i * 10,
 				});
-				await Bun.sleep(5);
+				await Bun.sleep(40);
 			}
 			return singleResult(options, { output: "done" });
 		});
 
 		const ops: string[] = [];
-		using idle = new IdleTimeout(40);
+		// Timing invariant (keep, do not re-tighten): total mock work (20*40ms = 800ms) > idle window (250ms) > scheduling jitter (~tens of ms).
+		using idle = new IdleTimeout(250);
 		const result = await runEvalAgent(
 			{ prompt: "investigate" },
 			{
diff --git a/packages/coding-agent/test/tools/edit-renderer.test.ts b/packages/coding-agent/test/tools/edit-renderer.test.ts
index f1ba84dcc..23f4207c0 100644
--- a/packages/coding-agent/test/tools/edit-renderer.test.ts
+++ b/packages/coding-agent/test/tools/edit-renderer.test.ts
@@ -281,9 +281,10 @@ describe("editToolRenderer", () => {
 			const component = new ToolExecutionComponent("edit", { input }, { snapshots }, hashlineTool, uiStub, tmpDir);
 
 			component.setArgsComplete();
-			await Bun.sleep(50);
 
-			const rendered = Bun.stripANSI(component.render(160).join("\n"));
+			// The preview diff computes asynchronously after args complete; poll
+			// instead of a fixed sleep so the slower CI VM has time to finish it.
+			const rendered = await waitForRenderedText(component, 160, "export const b = 22;");
 			expect(rendered).toContain("export const b = 22;");
 			expect(rendered).not.toContain("No changes would be made");
 		} finally {