Update Elixir Dependencies (Strict Checklist)

This skill is intentionally written as a no-skip checklist. Agents must follow it exactly.

Non-negotiables (DO NOT SKIP)

You may update all dependencies marked "Update possible" in a single batch.
Any dependency that is blocked only by the project's mix.exs version constraint is NOT truly blocked. It must be moved into the update batch by changing the constraint.
Review diffs individually for each dependency being updated (even in a batch).
After updating dependencies, run the verification gates:
- mix compile --warnings-as-errors (must pass for both dev and test environments)
- mix format --check-formatted
- mix test
If any gate fails: STOP, fix, re-run the failing gate(s) until green, then continue.
Never "force" blocked updates caused by transitive constraints. Report them instead.

Step 0: Identify candidates

Run:

mix hex.outdated

Separate dependencies into two groups initially:

Update possible: dependencies where Latest > Current and status shows "Update possible"
Update not possible: dependencies showing "Update not possible"

Then, for each dependency in Update not possible, you MUST determine whether it is blocked by:

the project's own mix.exs constraint (fixable), or
transitive constraints (not fixable without larger coordination)

Do this classification with:

mix hex.outdated dep

Re-classify Update not possible dependencies into:

Constraint-only blocked (treat as updatable): output indicates it is blocked by the project's version constraint in mix.exs
Transitively blocked (truly blocked): output indicates other deps/constraints prevent the update

Step 1: Batch update all updatable dependencies

The batch list is:

all Update possible deps, plus
all Constraint-only blocked (treat as updatable) deps

1A) Review diffs for each dependency (required, do this BEFORE updating)

For each dependency dep in the batch list:

Record current_version and latest_version from mix hex.outdated.
Try: mix hex.package diff dep current_version..latest_version
If the diff command fails, you must still assess changes by reviewing:
- Hex package page release notes/changelog (or repository releases)
While reviewing, specifically look for:
- API changes (renames, arity changes, removed functions)
- config changes (new required keys, renamed keys, default changes)
- behavior changes (error/exception changes, validation changes, callback changes)
Note any breaking changes that will require code/config updates.

1B) Update all constraints in mix.exs

Edit mix.exs and update each dependency's version constraint to allow its latest_version (prefer pinning to the shown latest if feasible).
This MUST include any deps previously reported as blocked only by the project's mix.exs constraint.

1C) Fetch and lock

Run mix deps.get once to update the lock file for all dependencies.

1D) Apply required code changes

Make code/config changes needed for each updated dependency based on the diffs reviewed in step 1A.

1E) Verification gates (MUST be green before continuing)

Run in order:

mix compile --warnings-as-errors (dev environment)
MIX_ENV=test mix compile --warnings-as-errors (test environment)
mix format --check-formatted
mix test

If any step fails: STOP, fix the cause, then re-run from the failing step onward until all steps are green.

Step 2: Handle blocked dependencies

For any dependency classified as Transitively blocked (truly blocked):

Do not force. Report:
- dependency name + latest version
- which dependency is blocking it
- the exact conflicting version requirement/constraint

Step 3: Final confirmation and report