[ousamabenyounes]

Summary

• fail immediately when file-based discovery is configured without symfony/finder
• preserve custom discoverers, which do not require Finder
• cover the missing optional dependency in an isolated regression test
• update the docs that described the old skip-and-warn behavior
• add a [BC Break] changelog entry

Fixes #398.

Test verification (RED → GREEN)

Reproduced on unmodified main with production-only dependencies:

BUG: build succeeded with Mcp\Server

With the regression test present and the production fix reverted (RED):

Failed asserting that exception of type "Mcp\Exception\RuntimeException" is thrown.
FAILURES!
Tests: 1, Assertions: 2, Failures: 1.

With the fix applied (GREEN):

OK (1 test, 3 assertions)

Full local validation:

Composer validation: passed
PHP CS Fixer: passed
PHPStan: passed
PHPUnit unit: OK (2669 tests, 8695 assertions)
PHPUnit integration: OK (108 tests, 292 assertions)
Changed executable line coverage: 2/2

[ousamabenyounes]

Updated to 45b7fd5d448f7b456a863bce5ba5bc148a700df9.

• Merged current main into the branch. The only conflict was the import block in tests/Unit/Server/BuilderTest.php, resolved by keeping both sets of imports.
• docs/index.md and docs/run/server-builder.md on main still said discovery is skipped with a warning when symfony/finder is missing. They now say build() throws, unless a custom discoverer is set.
• Added a 0.10.0 [BC Break] changelog entry, as CONTRIBUTING.md asks for every break. 0.9.0 is already released.
• There were no review threads to address.

Validation:

• On merged main with the fix reverted, the regression test fails ("exception of type RuntimeException is thrown"). With the fix it passes (1 test, 3 assertions).
• Locally (PHP 8.5): composer validate, CS Fixer, PHPStan, unit (2669 tests) and integration (108 tests) all pass. Changed production lines are 2/2 covered.
• All pipeline and Documentation checks pass on this SHA.

[ousamabenyounes]

Resolved the conflict with main by preserving both the new session 404 changelog entry and this PR’s discovery BC-break entry. The discovery failure, regression test, and documentation remain intact on current main.

The regression test fails on 5d311d69 because no RuntimeException is thrown and passes after the fix (1 test, 3 assertions). Local run-ci.sh is iso-better than baseline: style, PHPStan, docs, unit (2696), integration (108), and 2/2 changed-line coverage pass; identical pre-existing interop failures remain.

Local CI is not green. GitHub CI is green. Pushed in 0b9b845f008d.