fix(worker): relabel rewriter tags after cross-backend reshape (#113)

[Varashi]

Summary

Closes #113. After a cross-backend reshape onto NVENC, the rewriter executes the CUDA branch (`inlineass(CUDA)`, `tonemap_cuda`) but the emitted tags still showed VAAPI-canonical names — so the 320/320 nvenc qa_matrix pass logged `hw-decode:filter:opencl-tonemap->vaapi:inlineass-vaapi` even though the actual filter graph was `tonemap_cuda + inlineass(CUDA)`.

The output was correct; the tag strings misrepresented the executed graph.

What changed

• New `relabelCrossBackendTags(tags)` in `worker/agent/rewriter_tags.go` — detects `cross-backend:*->X` and rewrites VAAPI-named substrings (`inlineass-vaapi`, `bitmap-inlineass-vaapi`, `opencl-tonemap->vaapi`, `tonemap_opencl-normalized`) to the X target's names. NVENC mapping ships; same-backend / unknown-target are no-ops.
• Called from `worker/agent/main.go` right before `log.Printf("rewriter applied: ...")` — only the log + matrix consumers see the tags, so a string-level rewrite is safe.
• Unit tests in `rewriter_tags_relabel_test.go` cover the prod-shape tag list, bitmap+HDR-tonemap prefix tag, SW-tonemap normalized tag, and the three no-op cases (no marker / target=vaapi / unknown target).

Test plan

• `go build ./...` clean
• `go test` — new tests + existing `TestRewriterTagInventory` green
• CodeRabbit pass

🤖 Generated with Claude Code

Summary by CodeRabbit

• Bug Fixes

  • Enhanced tag post-processing to correctly retarget and relabel tags when executing rewrite operations across different execution backends, ensuring logs and metrics reflect the actual backend in use.

• Tests

  • Added comprehensive test coverage for cross-backend tag relabeling including both successful relabeling and no-op verification scenarios.

[coderabbitai]

📝 Walkthrough

Walkthrough

Adds relabelCrossBackendTags helper to post-process filter tags during cross-backend rewrite. Extracts target backend from cross-backend:*->X markers and rewrites VAAPI-canonical substrings to CUDA/NVENC equivalents. Integrated into handleTask rewriter path with comprehensive unit tests.

Changes

Cross-backend tag relabeling for NVENC rewrite

Layer / File(s)	Summary
Relabeling logic and test coverage worker/agent/rewriter_tags.go, worker/agent/rewriter_tags_relabel_test.go	relabelCrossBackendTags extracts target from cross-backend:*->X tags and performs ordered string rewrites for supported targets (nvenc), replacing VAAPI-canonical substrings (e.g., inlineass-vaapi, tonemap_vaapi) with CUDA equivalents. No-ops when marker missing, target empty, or target is canonical vaapi. Tests cover NVENC relabeling with multiple tag patterns and no-op cases (no marker, canonical target, unknown target).
Integration with rewriter pipeline worker/agent/main.go	handleTask calls relabelCrossBackendTags(res.Changes) post-rewrite to ensure tags match the executed backend before logging and emission.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~12 minutes

Possibly related PRs

• Varashi/scaleplex#81: Renames NVIDIA dialect from "nvidia" to canonical "nvenc" (with "nvidia" alias), aligning the target backend value recognized by relabelCrossBackendTags.
• Varashi/scaleplex#83: Implements reshapeForeignHWArgv that emits cross-backend:<src>-><dst> change tags consumed by this PR's relabeling logic.
• Varashi/scaleplex#89: Adds cross-backend rewriter behavior and TagReplaceForeignInitHWDevice tag emission; this PR post-processes those tags to match execution context.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 75.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	Title accurately summarizes the main change: relabeling rewriter tags post-reshape to reflect actual executed backend, directly addressing issue #113.
Linked Issues check	✅ Passed	Changes fully satisfy #113 requirements: detects cross-backend markers, rewrites VAAPI filter tags to target backend (NVENC/CUDA), calls relabel in tag emission path, includes comprehensive unit tests.
Out of Scope Changes check	✅ Passed	All changes scoped to issue #113: relabelCrossBackendTags function, invocation in handleTask, and tests. No unrelated modifications or scope creep.

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Warning

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🔧 golangci-lint (2.12.2)

level=error msg="[linters_context] typechecking error: pattern ./...: directory prefix . does not contain modules listed in go.work or their selected dependencies"

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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 `@worker/agent/rewriter_tags_relabel_test.go`:
- Around line 52-62: Add a new table-driven test entry in
rewriter_tags_relabel_test.go that verifies relabeling of OpenCL tonemap to
VAAPI: include an input tag "filter:tonemap_opencl" (and any companion tags
needed by the existing table shape) and assert the expected output contains
"filter:tonemap_vaapi" and "force-output-format-vaapi" (or document an explicit
no-op if that's the intended behavior); place it alongside the existing cases
(e.g., near the "SW-tonemap normalized tag" case) so the test enforces the
contract for the OpenCL→VAAPI relabeling path.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

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

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: ASSERTIVE

Plan: Pro Plus

Run ID: 70a54d76-efb6-4d36-83a8-5318570cc932

📥 Commits

Reviewing files that changed from the base of the PR and between 71ce3ff and 2d9560e.

📒 Files selected for processing (3)

• worker/agent/main.go
• worker/agent/rewriter_tags.go
• worker/agent/rewriter_tags_relabel_test.go

[coderabbitai]

🧹 Nitpick | 🔵 Trivial | ⚡ Quick win

Add a case for filter:tonemap_opencl->tonemap_vaapi / force-output-format-vaapi.

Tied to the rep coverage gap above. If those tags reach the nvenc path, a row asserting they relabel (or a documented no-op) locks the contract.

🤖 Prompt for 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.

In `@worker/agent/rewriter_tags_relabel_test.go` around lines 52 - 62, Add a new
table-driven test entry in rewriter_tags_relabel_test.go that verifies
relabeling of OpenCL tonemap to VAAPI: include an input tag
"filter:tonemap_opencl" (and any companion tags needed by the existing table
shape) and assert the expected output contains "filter:tonemap_vaapi" and
"force-output-format-vaapi" (or document an explicit no-op if that's the
intended behavior); place it alongside the existing cases (e.g., near the
"SW-tonemap normalized tag" case) so the test enforces the contract for the
OpenCL→VAAPI relabeling path.