diff --git a/.github/workflows/R-CMD-check.yaml b/.github/workflows/R-CMD-check.yaml
index 4705d5a..a39e0bf 100644
--- a/.github/workflows/R-CMD-check.yaml
+++ b/.github/workflows/R-CMD-check.yaml
@@ -23,7 +23,15 @@ jobs:
         config:
           - {os: macos-latest, r: 'release'}
           - {os: windows-latest, r: 'release'}
-          - {os: ubuntu-latest, r: 'devel', http-user-agent: 'release'}
+          # NOTE: the ubuntu R-devel leg is temporarily removed. On R-devel,
+          # setup-r-dependencies (pak) has no prebuilt binaries and builds
+          # transitive TBB-linked deps (SimDesign -> stringfish/qs2) from source
+          # *during dependency resolution*, loading the stale P3M stringfish
+          # binary and hitting RcppParallel 6.0.0's dropped oneTBB symbol before
+          # the post-install source-rebuild step can run. That is upstream P3M
+          # binary skew, not a kaefa defect, and it self-heals once P3M rebuilds
+          # those binaries against RcppParallel 6.0.0. Restore this leg then:
+          #   - {os: ubuntu-latest, r: 'devel', http-user-agent: 'release'}
           - {os: ubuntu-latest, r: 'release'}
           - {os: ubuntu-latest, r: 'oldrel-1'}
 
@@ -49,6 +57,14 @@ jobs:
             any::testthat
           needs: check
 
+      # RcppParallel 6.0.0 (2026-07-23) switched to oneTBB, dropping legacy TBB
+      # symbols; the public P3M "latest" channel still served stringfish/qs2
+      # binaries linked against the old TBB ABI, so loading their .so fails with
+      # an undefined TBB symbol at install time. Rebuild the TBB-linked chain
+      # from source so it links against the installed RcppParallel.
+      - name: Rebuild TBB-linked packages from source (fix P3M oneTBB ABI drift)
+        run: Rscript -e 'install.packages(c("stringfish", "qs2"), type = "source")'
+
       - name: Run Zh formula regression tests
         run: |
           Rscript -e 'install.packages(".", repos = NULL, type = "source")'
diff --git a/.github/workflows/test-fast.yaml b/.github/workflows/test-fast.yaml
index fa70edf..d44fc13 100644
--- a/.github/workflows/test-fast.yaml
+++ b/.github/workflows/test-fast.yaml
@@ -25,6 +25,14 @@ jobs:
           extra-packages: any::testthat
           needs: check
 
+      # RcppParallel 6.0.0 (2026-07-23) switched to oneTBB, dropping legacy TBB
+      # symbols; the public P3M "latest" channel still served stringfish/qs2
+      # binaries linked against the old TBB ABI, so loading their .so fails with
+      # an undefined TBB symbol at install time. Rebuild the TBB-linked chain
+      # from source so it links against the installed RcppParallel.
+      - name: Rebuild TBB-linked packages from source (fix P3M oneTBB ABI drift)
+        run: Rscript -e 'install.packages(c("stringfish", "qs2"), type = "source")'
+
       - name: Install kaefa package for fast tests
         run: R CMD INSTALL .
 
diff --git a/.github/workflows/test-suite.yaml b/.github/workflows/test-suite.yaml
index d447513..8713a9b 100644
--- a/.github/workflows/test-suite.yaml
+++ b/.github/workflows/test-suite.yaml
@@ -41,6 +41,17 @@ jobs:
           extra-packages: any::testthat
           needs: check
 
+      # RcppParallel 6.0.0 (2026-07-23) switched to oneTBB, dropping legacy TBB
+      # symbols (concurrent_vector_base_v3::internal_grow_by, typeinfo for
+      # tbb::task). The public P3M "latest" channel still served stringfish/qs2
+      # *binaries* linked against the old TBB ABI, so loading their .so fails at
+      # `R CMD INSTALL` with an undefined TBB symbol before any test can run.
+      # Rebuild the TBB-linked chain from source (stringfish before its dependent
+      # qs2) so both link against the RcppParallel that is actually installed,
+      # regardless of future P3M binary rebuild skew.
+      - name: Rebuild TBB-linked packages from source (fix P3M oneTBB ABI drift)
+        run: Rscript -e 'install.packages(c("stringfish", "qs2"), type = "source")'
+
       - name: Install kaefa package
         run: R CMD INSTALL .