fix: refuse an input whose table would fall in the reserved _filesql_ namespace

[nao1215]

v0.43.0 began hiding _filesql_ tables from DumpDatabase and from the table listings this package returns, so the metadata table it writes does not show up as a user table. It did not stop a caller's input from landing in that namespace: a file named _filesql_report.csv still loaded, and the resulting table answered queries while being absent from every listing and from any dump — its rows were silently left out of an export, which is worse than the load failing.

A prefix is only reserved if nothing else can occupy it, so an input whose table name would begin with _filesql_ is now refused with ErrReservedTableName, naming the table and the prefix. SQLite answers the same way for its own sqlite_ prefix, and the rule follows that precedent. It covers every way a name is chosen: a path, a reader's explicit table name, an Excel sheet, and an ACH or Fedwire base name. A name that merely resembles the prefix, such as filesql_report, is unaffected — the check is a prefix match, not the LIKE pattern used for hiding.

This also makes the rule sqly relies on true: it can filter the prefix out of its own .tables listing knowing that no user table can be hidden by the filter.

Summary by CodeRabbit

• New Features

  • Added validation for reserved table names beginning with _filesql_.
  • Added ErrReservedTableName to identify rejected table-name inputs.
  • Similar names without the leading underscore, such as filesql_report, remain valid.

• Documentation

  • Updated ACH/Fedwire guidance and the changelog to explain reserved table-name rules.

• Bug Fixes

  • Reserved names are rejected before data parsing, buffering, or database changes occur.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: 0c2856b6-7070-414b-84e9-33d4555632bc

📥 Commits

Reviewing files that changed from the base of the PR and between 2ecf0c4 and 5bc4dce.

📒 Files selected for processing (3)

• CHANGELOG.md
• source_registry.go
• source_registry_test.go

🚧 Files skipped from review as they are similar to previous changes (3)

• source_registry_test.go
• CHANGELOG.md
• source_registry.go

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📝 Walkthrough

Walkthrough

The package now reserves table names beginning with _filesql_. It exposes ErrReservedTableName, validates names before ingestion or table creation, documents the rule, and tests rejection of reserved names alongside acceptance of lookalike names.

Changes

Reserved table names

Layer / File(s)	Summary
Reserved-name contract and coverage errors.go, source_registry.go, source_registry_test.go, CHANGELOG.md, README.md, ach.go	The package defines ErrReservedTableName, rejects names beginning with _filesql_, documents the reserved namespace, and tests reserved and lookalike names.
Ingestion-path validation ach.go, wire.go, stream_processor.go	ACH, Fedwire, reader, and XLSX ingestion paths validate sanitized table names before parsing, buffering, database checks, or table creation.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Possibly related PRs

• nao1215/filesql#185: Related to validation of sanitized table names.
• nao1215/filesql#194: Related to XLSX table-name handling.
• nao1215/filesql#303: Related to reserved _filesql_ table handling.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely describes the primary change: rejecting inputs whose table names use the reserved _filesql_ namespace.
Description check	✅ Passed	The description clearly explains the problem, intended behavior, affected input paths, error behavior, and valid lookalike names.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/reserve-filesql-table-prefix

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[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@source_registry.go`:
- Around line 176-180: Update validateTableName to normalize tableName and
compare it case-insensitively with sourceTablePrefix, matching SQLite LIKE
behavior while preserving the existing reserved-name error. Add a case-variant
regression case to TestReservedTableNameIsRefused.

🪄 Autofix

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: cccd43fc-94f3-43f0-8551-16f56d4eb2c0

📥 Commits

Reviewing files that changed from the base of the PR and between 27bc6fe and 2ecf0c4.

📒 Files selected for processing (8)

• CHANGELOG.md
• README.md
• ach.go
• errors.go
• source_registry.go
• source_registry_test.go
• stream_processor.go
• wire.go

[github-actions]

Code Metrics Report

	main (27bc6fe)	#306 (d100907)	+/-
Coverage	90.3%	90.3%	-0.1%
Test Execution Time	14s	14s	0s

Details

  |                     | main (27bc6fe) | #306 (d100907) |  +/-  |
  |---------------------|----------------|----------------|-------|
- | Coverage            |          90.3% |          90.3% | -0.1% |
  |   Files             |             64 |             64 |     0 |
  |   Lines             |          10520 |          10535 |   +15 |
+ |   Covered           |           9507 |           9519 |   +12 |
  | Test Execution Time |            14s |            14s |    0s |

Code coverage of files in pull request scope (79.0% → 79.0%)

Files	Coverage	+/-	Status
ach.go	86.8%	-0.5%	modified
errors.go	100.0%	0.0%	modified
source_registry.go	87.5%	+1.5%	modified
stream_processor.go	73.4%	+0.0%	modified
wire.go	79.6%	-1.1%	modified

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Reported by octocov