Fixes#18237Implements the proposed solution from the issue:When users run `terraform init` locally on a different OS/architecturethan their Coder instance, the generated .terraform.lock.hcl file maybe missing provider hashes for the target platform. This causes Terraformto modify the lock file during provisioning and download providers fromthe internet on every workspace build instead of using the shared cache,significantly slowing down provisioning.## ImplementationThis change implements the proposed solution:1. **Record the checksum** of .terraform.lock.hcl before running terraform init2. **Compare checksums** after terraform init completes3. **Warn the user** if the checksum changes, with actionable guidance## Changes- Added `checksumFile()` function to calculate SHA256 checksums- Added `getTerraformLockFilePath()` helper function- Modified `init()` to:  - Calculate lock file checksum before running terraform init  - Calculate lock file checksum after terraform init  - Call `warnLockFileModified()` if checksums differ- Created `warnLockFileModified()` that:  - Logs a warning for observability  - Displays a prominent, actionable warning to users with:    - Clear explanation of the problem and its impact    - Multi-platform solution (linux_amd64, linux_arm64, darwin_amd64, darwin_arm64, windows_amd64)    - Single-platform quick fix option    - Link to official documentation- Added comprehensive tests:  - `TestChecksumFile`: validates checksum calculation and change detection  - `TestGetTerraformLockFilePath`: validates path construction  - `TestWarnLockFileModified`: validates warning message content## Advantages Over Alternative ApproachesThis checksum-based approach (as proposed in the issue):- ✅ Detects ANY lock file modification, not just specific messages- ✅ Works regardless of Terraform version or output format changes- ✅ Simple, reliable implementation- ✅ No parsing of Terraform output required- ✅ Catches edge cases where Terraform modifies lock file without the expected messageThe warning message provides both:- Multi-platform command for teams with mixed OS/arch- Single-platform command for quick fix targeting just Coder's platform

Fixes#18237When users run `terraform init` locally on a different OS/architecturethan their Coder instance, the generated .terraform.lock.hcl file maybe missing provider hashes for the target platform. This causes Terraformto download providers from the internet on every workspace build insteadof using the shared cache, significantly slowing down provisioning.## SolutionThis change detects when the lock file is modified during `terraform init`by comparing CRC32 checksums before and after. When a change is detected,a concise warning is displayed with the exact command to fix the issue.## Implementation- Added `checksumFileCRC32()` function to calculate CRC32 checksums  - Uses CRC32 instead of SHA256 for speed (lock files are small)  - Returns 0 if file doesn't exist or can't be read- Modified `init()` to:  - Calculate lock file checksum before running terraform init  - Calculate lock file checksum after terraform init  - Call `warnLockFileModified()` if checksums differ- Created `warnLockFileModified()` that:  - Logs a warning for observability  - Displays a concise WARN message with:    - Brief explanation of the problem    - Exact command to fix with multiple platform targets- Added tests:  - `TestChecksumFileCRC32`: validates checksum calculation and change detection  - `TestWarnLockFileModified`: validates warning message content## Example Warning```WARN: .terraform.lock.hcl was modified during init. This means provider hashesare missing for the current platform (linux_amd64). Update the lock file with:  terraform providers lock -platform=linux_amd64 -platform=linux_arm64 -platform=darwin_amd64 -platform=darwin_arm64 -platform=windows_amd64```## Advantages- ✅ **Detects any lock file modification** - not dependent on Terraform output format- ✅ **Fast CRC32 checksum** - optimized for small files- ✅ **Concise warning** - gets straight to the point- ✅ **Copy-paste ready command** - users know exactly what to run- ✅ **Multi-platform by default** - prevents future issues

The checksumFileCRC32 function signature was updated to include context.Contextand slog.Logger parameters. Updated the test to pass these required arguments.

- Use testutil.Context with WaitShort timeout instead of context.Background- Replace slog.Make() with testutil.Logger(t)- Use hardcoded expected checksum (0x08f39f51) instead of calling  checksumFileCRC32 twice for comparison- Move context and logger creation into each subtest