Pin the aarch64 Miniforge installer to unbreak Linux aarch64 wheel builds (#8602)

[atalman]

Summary

Linux aarch64 nightly wheel builds have been failing since 2026-08-21 for the domain
libraries (torchvision, torchaudio, ao, executorch). Nothing in any PyTorch repository
changed.

build_wheels_linux.yml bootstraps conda on aarch64 by downloading Miniforge from the
releases/latest pointer. That pointer is mutable. It moved, and the newer installer puts
the base environment on Python 3.14. The shared setup-binary-builds action then runs
conda install -y conda=25.3.0, and conda 25.3.0 has no Python 3.14 build, so the solve is
unsatisfiable:

LibMambaUnsatisfiableError: Encountered problems while solving:
  - package conda-25.3.0-py310h4c7bcd0_0 requires python >=3.10,<3.11.0a0, but none of the providers can be installed
...
Pins seem to be involved in the conflict. Currently pinned specs:
 - python=3.14

This step runs in the base environment before the target environment is created, so all
target Python versions fail identically. In the last torchvision aarch64 nightly, 80 of 81
jobs failed, every one of them at this step.

From the job logs:

when (UTC)	what the installer produced	conda install -y conda=25.3.0
2026-08-20 19:49	conda 26.3.2, base Python 3.13	succeeded, as a downgrade
2026-08-21 11:48	conda 26.5.3, base Python 3.14	fails

Miniforge 26.5.3-0 was published on 2026-08-15, but releases/latest still served 26.3.2 on
08-20 at 19:49 and served 26.5.3 by 08-21 at 11:48. The pointer moved on its own, days after
that release already existed, which is why this broke with no commit behind it.

Fix

Pin the installer to 26.3.2-3, the release that was last green, and add -f to the curl.

This restores exactly the base environment the last green run had. Verified by downloading
the tagged aarch64 asset and comparing package build strings against the last green job log:

| package | last green run | in the 26.3.2-3 asset | | --- | --- | --- |
| conda | 26.3.2-py313hd81a959_1 | yes |
| conda-libmamba-solver | 26.4.2-pyhd8ed1ab_0 | yes | | libmambapy | 2.5.0-py313h44afa9f_0 | yes |
| mamba | 2.5.0-hd347465_0 | yes |
| openssl | 3.6.2-h546c87b_0 | yes |
| python | 3.13.13-h11c0449_100_cp313 | yes |

The tagged release publishes the asset under the same unversioned filename, so only the path
segment of the URL changes.

The -f matters now that the URL carries a hand written tag. Without it, curl treats a 404 as
a successful transfer, writes the error body into the installer file and exits 0. chmod +x
then succeeds and the shell executes the error page, which reports a syntax error on line 1
and exit 127 instead of a download failure.

Why not change the conda pin instead

The guard in setup-binary-builds is if [[ "${RUNNER_OS}" != "macOS" ]], which keys on the
operating system rather than on whether the base environment actually needs the pin. aarch64
is now a counter-example, so that guard is worth revisiting. It should not be revisited in
this change:

• On aarch64 the pin is a downgrade, so skipping it hands the Python 3.15 solve to conda
  26.5.3. Python 3.15 resolves from the conda-forge/label/python_dev and conda-forge/label/python_rc pre-release labels, and the only note in this repository about
  a newer base conda against those labels is the comment in the macOS branch saying it returns

400. 20 of torchvision's 81 aarch64 jobs are 3.15 or 3.15t, and all of them were green with
     the pin in place.

• Keeping the pin only for 3.15 does not work either, because that reinstalls conda 25.3.0 on
  a Python 3.14 base, which is the failure above.
• Bumping the pin for everyone was already proposed in [macOS CI] Bump pinned conda to 26.5.3 to fix osx-arm64 nightly builds (base env now Python 3.14) #8284 and dropped before merge. The
  comment added there records that upgrading the Linux and Windows containers yields
  NoChannelsConfiguredError.

A good follow-up is to measure whether conda 26.5.3 can resolve python=3.15.0b4 from those
two labels on linux-aarch64. If it can, the pin can be skipped on aarch64 and the installer
can float again. If it cannot, the pin stays and the real reason for it should be written down,
because the comment above it currently gives a reason that does not hold on aarch64.

Test plan

What was checked before opening this:

• x86_64, Windows and macOS cannot be affected. The changed step is gated on
  inputs.architecture == 'aarch64', and setup-binary-builds is not touched.
• The 26.3.2-3 release publishes Miniforge3-Linux-aarch64.sh under the same filename this
  step already uses.
• The package build strings in that asset match the last green run, as listed above.
• curl behaviour with and without -f on a 404 was reproduced locally against a local server.

What still needs CI, and what a reviewer should look for:

• One aarch64 wheel build on this branch. In the log, the installer should report conda
  26.3.2, and conda install -y conda=25.3.0 should solve. A 3.15 job is the most valuable
  one to include.
• This has not been run through an aarch64 nightly yet, so that confirmation is still open.

Authored with assistance from Claude Code (AI assistant).

(cherry picked from commit 2f89f62)

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1 Skipped Deployment

Project	Deployment	Actions	Updated (UTC)
torchci	Ignored		Aug 21, 2026 6:36pm