feat(http-client)\!: complete hishel 1.x migration with breaking config changes

[hartym]

Summary

Completes the migration from hishel 0.1.x to 1.x by implementing the new SpecificationPolicy/CacheOptions API and updating all configuration formats. This is the third and final phase of the migration, addressing #784.

⚠️ This PR contains BREAKING CHANGES and requires manual testing before merge.

Migration Phases Completed

• ✅ Phase 1: Import path fixes (hishel._async → hishel._async_httpx, etc.)
• ✅ Phase 2: Core data model migration (Entry/EntryMeta/AsyncBaseStorage)
• ✅ Phase 3 (this PR): Configuration API and policy system migration

Key Metrics

• Files Changed: 24 files
• Net Impact: +510/-468 lines (42 net additions)
• Risk Level: 🟠 High
• Estimated Review Time: ~45 minutes
• Test Coverage: All existing tests passing + new validation tests

---

🔴 Breaking Changes

Configuration API Changes

The cache configuration structure has been significantly updated to align with hishel 1.x's policy-based architecture:

1. Configuration Key Renamed

# ❌ OLD (hishel 0.1.x)
http_client:
  cache:
    controller:
      type: hishel.Controller
      
# ✅ NEW (hishel 1.x)
http_client:
  cache:
    policy:
      type: hishel.SpecificationPolicy

2. CacheOptions Replaces Controller Arguments

# ❌ OLD
http_client:
  cache:
    controller:
      allow_stale: true
      allow_heuristics: true
      cacheable_methods: [GET, HEAD]
      cacheable_status_codes: [200, 301, 308]

# ✅ NEW  
http_client:
  cache:
    policy:
      arguments:
        cache_options:
          allow_stale: false          # default: false
          supported_methods: [GET, HEAD]  # renamed from cacheable_methods
          shared: true                # default: true (new parameter)

3. Removed Parameters (RFC 9111 Compliance)

These parameters are no longer configurable as hishel 1.x strictly follows RFC 9111:

• ❌ allow_heuristics - Heuristic caching is always RFC 9111 compliant
• ❌ cacheable_status_codes - Status code cacheability determined by RFC 9111

Migration Support

Users with old configuration will receive a helpful error message with complete migration guide:

ValueError: The 'controller' configuration key has been removed in hishel 1.x.
Please use 'policy' instead.

Migration guide:
  Old (hishel 0.1.x):
    http_client:
      cache:
        controller:
          type: hishel.Controller
          arguments:
            allow_stale: false
            cacheable_methods: [GET, HEAD]

  New (hishel 1.x):
    http_client:
      cache:
        policy:
          type: hishel.SpecificationPolicy
          arguments:
            cache_options:
              shared: true
              supported_methods: [GET, HEAD]
              allow_stale: false

Note: 'allow_heuristics' and 'cacheable_status_codes' are no longer configurable.
      Caching behavior is now strictly RFC 9111 compliant.

---

🔧 What Changed

🎨 Configuration Changes

• Renamed: http_client.cache.controller → http_client.cache.policy
• Added: Pydantic model validator with comprehensive migration error
• Updated: All configuration documentation and examples
• Fixed: Service DI to properly instantiate CacheOptions as separate service

🐛 Bug Fixes

• Response serialization: Handle both httpcore Response (has content) and hishel Response (needs aread())
• Test discovery: Exclude misc/ worktree templates that were incorrectly being tested
• ParseError handling: Define locally after hishel removed it from public API

📝 Documentation Updates

• docs/apps/http_client/examples/cache.yml - Updated to new policy format
• docs/apps/http_client/examples/full.yml - Complete migration guide with comments
• Test snapshots regenerated to reflect new configuration structure

🏗️ Technical Implementation

Core Files Modified:

• harp_apps/http_client/settings/cache.py - New policy-based configuration with validator
• harp_apps/http_client/services.yml - CacheOptions as separate service with DI
• harp_apps/http_client/contrib/hishel/adapters.py - Response serialization fix
• harp/config/tests/test_all_applications_settings.py - Fixed test discovery

Constants Migration:

# Migrated to local constant (no longer in hishel 1.x public API)
HEURISTICALLY_CACHEABLE_STATUS_CODES = (200, 203, 204, 206, 300, 301, 308, 404, 405, 410, 414, 501)

---

✅ Backwards Compatibility

What Still Works

• ✅ Cached data: All cache entries from hishel 0.1.x remain fully readable
• ✅ Default configuration: No config changes needed if using defaults
• ✅ Storage layer: HARP's blob storage integration unchanged

What Breaks

• ❌ Custom cache configuration: Must update YAML files to new format
• ❌ Controller references: Must rename to policy throughout codebase

---

🧪 Testing Strategy

Test Coverage

✅ Unit Tests: 19/19 passing (harp_apps/http_client/tests/)
✅ Config Tests: 10/10 passing (test_all_applications_settings.py)  
✅ Example Tests: 42/42 passing (test_all_examples.py)
✅ Integration: Response serialization verified
✅ Validation: Migration error message tested

Manual Testing Required

Before merging, please verify:

Cache Functionality

• Cache hits/misses working correctly
• Cache headers respected (Cache-Control, Expires, etc.)
• Stale response handling per RFC 9111
• GET/HEAD method caching works
• Other methods correctly bypass cache

Migration Path

• Old configuration properly rejected with helpful error
• New configuration loads successfully
• Default configuration works without changes
• Custom CacheOptions can be configured

Storage Integration

• Cached entries persist correctly
• Old cache entries still readable
• Cache invalidation works
• Storage backend (SQL/Redis/Memory) integration stable

Performance

• No performance regression in cache operations
• Memory usage remains reasonable
• Response serialization not slower

---

📊 Risk Assessment

Overall Risk: 🟠 High (6.5/10)

Factor	Score	Details
Size	4/10	Moderate: 24 files, ~500 lines changed
Complexity	8/10	Core caching system with DI integration
Test Coverage	3/10	All existing tests pass, new validation added
Dependencies	7/10	Major version upgrade of caching library
Breaking Changes	9/10	Configuration format incompatible

Mitigation Strategies

1. Phased Rollout: Deploy to staging first, monitor cache metrics
2. Migration Support: Clear error messages guide users through upgrade
3. Rollback Plan: Can revert to hishel 0.1.x if critical issues found
4. Documentation: Complete migration guide in changelog and examples

---

🎯 Checklist

Code Quality

• Code follows project style guidelines (ruff passing)
• Self-review completed
• No debugging code left
• Type hints maintained

Testing

• All existing tests passing
• New validation tests added
• Test snapshots updated
• No flaky tests introduced

Documentation

• Breaking changes documented in changelog
• Migration guide provided with examples
• Configuration examples updated
• Error messages are clear and actionable

Configuration

• Backwards incompatibility explicitly called out
• Migration validator prevents silent failures
• Default values sensible and documented

Dependencies

• hishel 1.x compatibility verified
• No security implications
• All internal API usage documented

---

📚 Additional Context

Architecture Decision

Why CacheOptions as Separate Service?

Initial attempts to nest CacheOptions within the policy service failed because HARP's DI container doesn't auto-instantiate nested Service objects. The solution creates CacheOptions as a separate service in services.yml and references it:

- name: "http_client.cache.policy"
  defaults:
    cache_options: !ref "http_client.cache.policy.options"

- name: "http_client.cache.policy.options"
  type: "hishel.CacheOptions"
  arguments:
    shared: true
    supported_methods: ["GET", "HEAD"]
    allow_stale: false

Related Issues & PRs

• Closes feat(http-client): migrate to hishel 1.x #784
• Depends on: hishel 1.x release (October 2025)
• Blocks: Future HTTP client improvements

Deployment Notes

• Requires configuration update for custom cache settings
• Recommend announcing breaking change in release notes
• Consider adding deprecation notice in 0.9.x before requiring 1.x

---

🚀 Next Steps After Merge

1. Deploy to staging environment for real-world testing
2. Monitor cache metrics for performance regressions
3. Gather user feedback on migration experience
4. Update main documentation with production examples
5. Consider backporting critical fixes to 0.9.x if needed

---

📝 Commit History

This PR includes 3 commits spanning the full hishel 1.x migration:

1. 2704b862 - Phase 1: Import path fixes
2. ed3b9ea8 - Phase 2: Entry/AsyncBaseStorage migration
3. 7f0e3011 - Phase 3: Configuration API and policy system (this PR)

Note: This is an initial implementation requiring thorough manual testing before merge.

[Copilot]

Pull request overview

This PR completes the migration from hishel 0.1.x to 1.0.x, representing the final phase of a three-part migration that modernizes HARP's HTTP caching implementation. The changes introduce a breaking architectural shift by extracting cache functionality into a dedicated http_cache application with updated configuration API.

Key Changes

• Created new http_cache application with hishel 1.0's policy-based architecture
• Migrated all cache-related code from harp_apps.http_client.contrib.hishel to harp_apps.http_cache
• Updated CLI commands: harp-proxy config → harp-proxy system config

Reviewed changes

Copilot reviewed 106 out of 114 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
pyproject.toml	Updated hishel dependency from ~0.1.1 to ~1.1.5
harp_apps/http_cache/init.py	New http_cache application module initialization
harp_apps/http_cache/settings.py	New settings using SpecificationPolicy instead of Controller
harp_apps/http_cache/services.yml	Service definitions for policy, storage, and transport
harp_apps/http_cache/adapters.py	Storage adapter migrated from http_client.contrib.hishel
harp_apps/http_cache/storages.py	AsyncStorage implementation for hishel 1.0 Entry API
harp_apps/http_cache/transports.py	AsyncCacheTransport with URL normalization for load balancing
harp_apps/http_client/settings/init.py	Removed CacheSettings, simplified to core client settings
harp_apps/http_client/services.yml	Removed cache service definitions (moved to http_cache)
harp/commandline/system.py	New system command group with config and services subcommands
harp/config/defaults.py	Added http_cache to default applications
docs/changelogs/unreleased.rst	Comprehensive changelog documenting breaking changes

Comments suppressed due to low confidence (6)

pyproject.toml:1

• The specified hishel version constraint '=1.1.5' may be incorrect. According to the PR description, this migration targets hishel 1.0.x (released October 2025), but version 1.1.5 would be a later minor release. Verify that version 1.1.5 exists and is the intended target, or consider using '=1.0.0' to match the 1.0.x series mentioned in the PR description.
  harp_apps/http_cache/adapters.py:1
• This conditional logic for handling different response types (httpcore vs hishel) uses duck typing with hasattr checks, which is fragile. Consider using isinstance() checks with proper type imports for more reliable type discrimination: if isinstance(response, HttpcoreResponse) vs isinstance(response, HishelResponse). This makes the code more explicit and less prone to breaking if response objects gain new attributes.
  harp_apps/http_cache/storages.py:1
• The update_entry method always returns None without attempting to update the entry, silently failing the update operation. If hishel 1.0 calls this method expecting updates to succeed, this could lead to cache inconsistencies. Either implement the method properly by maintaining a UUID-to-key mapping, or raise NotImplementedError to make the limitation explicit rather than silently failing.
  harp_apps/http_cache/storages.py:1
• The remove_entry method is implemented as a no-op (just pass), silently failing to remove cache entries. This could lead to cache entries never being removed when they should be (e.g., after invalidation). Similar to update_entry, either implement the method properly or raise NotImplementedError to make the limitation explicit.
  harp/config/configurables/service.py:1
• The docstring changed from 'This is not usually the base interface' to 'This is usually the base interface', but the comment text is incomplete (ends with 'and you'). The comment should be completed to provide full context about the base type field's purpose.
  harp_apps/http_cache/adapters.py:1
• The error message uses boolean expressions that will always evaluate to True/False in the f-string, making the message confusing (e.g., 'headers=False' instead of 'headers missing'). Consider improving readability: raise ValueError(f\"Cache entry incomplete: headers {'present' if headers else 'missing'}, body {'present' if body else 'missing'}\")

---

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[Copilot]

Pull request overview

Copilot reviewed 119 out of 128 changed files in this pull request and generated no new comments.

Comments suppressed due to low confidence (7)

pyproject.toml:1

• hishel version 1.1.5 does not exist. According to the PR description knowledge cutoff of January 2025, and the statement that hishel 1.0.x was released in October 2025, this version (1.1.5) would be from the future relative to the knowledge cutoff. Verify that this version exists or use the appropriate hishel 1.0.x version.
  misc/cache-tests/run-tests.sh:1
• The script redirects both stdout to /dev/null, which will hide errors during startup. Consider redirecting only stdout while preserving stderr: uv run harp-proxy server --file config.yml > /dev/null 2>&1 & or better yet, log to a file for debugging failed test runs.
  harp_apps/storage/worker.py:1
• This line stores the string "true" for cached responses but None otherwise. However, line 155 extracts cached as event.transaction.extras.get(\"cached\") which could be any truthy value (not just True/False). This could lead to storing "true" for values like 1, "yes", etc. Consider normalizing to boolean: cached = bool(event.transaction.extras.get(\"cached\")).
  harp_apps/proxy/controllers.py:1
• The parse_cache_control function expects a single string value but request_cache_control is obtained from request.headers.get(\"cache-control\") which could return None. If the header is None, this will cause a TypeError. Add a None check or default value before calling parse_cache_control.
  harp_apps/http_cache/adapters.py:1
• Reading the entire response content with aread() for every cache operation could be memory-intensive for large responses. Consider implementing streaming support or adding size limits to prevent memory exhaustion when caching large files.
  harp/commandline/system.py:1
• [nitpick] The imports are not grouped according to PEP 8 style guidelines. Standard library imports should be separated from third-party imports with a blank line. Place asyncio in one group and orjson (third-party) in another group.
  harp_apps/dashboard/frontend/package.json:1
• pnpm version 10.22.0 appears to be from a future date (December 2025) relative to the knowledge cutoff of January 2025. Verify that this version exists and is intended, or use a version that is currently available.

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