Implement heap integrity testing and add PMM stub for memory management

[Zaid-maker]

Summary by CodeRabbit

• Tests
  • Added an automated heap integrity test suite that injects corruption to verify allocator integrity detection (corrupted headers, alignment issues, unmerged free blocks, pointer regressions).
• Build / Chores
  • Test and coverage targets updated to build/run the new integrity tests and include them in coverage runs.
• Documentation
  • Docs and README updated to document the new tests and local build/test steps.
• Release
  • Kernel version incremented.

[coderabbitai]

Caution

Review failed

The pull request is closed.

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: ccdf6f0a-585e-40c7-81cb-ad6f775f0cec

📥 Commits

Reviewing files that changed from the base of the PR and between c32e3ab and 49a244f.

📒 Files selected for processing (4)

• README.md
• kernel/VERSION
• site/docs.html
• site/index.html

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📝 Walkthrough

Walkthrough

Adds conditional heap test hooks and a host-side heap integrity test binary plus a PMM stub, updates Makefile to build/run these tests and include them in coverage, and documents the new test artifacts and version bump.

Changes

Cohort / File(s)	Summary
Build Configuration kernel/Makefile	Adds building and running of heap_integrity_test and coverage-instrumented heap_integrity_test_cov; compiles src/heap.c with -DHEAP_ENABLE_TEST_HOOKS for host tests and includes tests/pmm_stub.c in test/link units.
Heap Test Hooks kernel/src/heap.c, kernel/src/heap.h	Introduces HEAP_ENABLE_TEST_HOOKS-guarded test scaffold: in-memory test arena, tracking arrays, and five debug APIs (heap_debug_seed_chain, heap_debug_corrupt_magic, heap_debug_misalign_size, heap_debug_make_next_regression, heap_debug_clear_chain) for seeding and mutating heap state.
Tests & Stubs kernel/tests/heap_integrity_test.c, kernel/tests/pmm_stub.c	Adds host test program that seeds chains, injects corruptions, calls heap_check_integrity() and asserts counters; adds minimal PMM stub implementing pmm_initialize/alloc/free/get_stats for test isolation.
Docs & Metadata README.md, site/*.html, kernel/VERSION	Updates build instructions, project layout and docs to include heap diagnostics/tests; updates site pages and increments kernel/VERSION to v0.0.20260331.1.

Sequence Diagram(s)

sequenceDiagram
    participant Test as "heap_integrity_test (host)"
    participant Heap as "kernel/src/heap (test hooks)"
    participant Checker as "heap_check_integrity"
    participant PMM as "pmm_stub"

    Test->>Heap: heap_debug_seed_chain(sizes, free_flags, count)
    Note right of Heap: builds synthetic blocks in test arena
    Test->>Heap: (optionally) heap_debug_corrupt_magic/index/misalign/next_regression
    Test->>Checker: heap_check_integrity(&report)
    Checker->>Heap: read block headers/pointers
    Checker->>PMM: (if queried) pmm_get_stats()
    Checker-->>Test: report (pass/fail, counters)
    Test->>Heap: heap_debug_clear_chain()

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Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Possibly related PRs

• Extract sbuf library and integrate unit testing #3: Modifies kernel/Makefile to add/extend host-side test targets—related to the Makefile changes that add/run heap_integrity_test.

Poem

🐇 I stitched a chain of blocks in sand and stone,
I nudged a magic byte to dance alone,
The checker sniffed the spoor and raised a bell—
Hooray, the rabbit found the bug and rang it well! 🥕✨

🚥 Pre-merge checks | ✅ 2 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately summarizes the main changes: implementing heap integrity testing and adding a PMM stub for memory management, matching the changeset content.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch heap-tests

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[codecov-commenter]

Codecov Report

❌ Patch coverage is 91.42857% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 67.47%. Comparing base (ce60547) to head (c32e3ab).

Files with missing lines	Patch %	Lines
kernel/src/heap.c	91.42%	3 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main       #9       +/-   ##
===========================================
- Coverage   99.26%   67.47%   -31.80%     
===========================================
  Files           3        4        +1     
  Lines         136      289      +153     
===========================================
+ Hits          135      195       +60     
- Misses          1       94       +93     

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